<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2022 Workiva-->
<!--r:56370811-1ea4-449b-b539-bf40027bbafa,g:a269f297-e559-4927-9073-3d3386baa22e-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://fivestarbank.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSHAREHOLDERSEQUITYUnaudited" xlink:type="simple" xlink:href="fsbc-20220930.xsd#CONSOLIDATEDSTATEMENTSOFCHANGESINSHAREHOLDERSEQUITYUnaudited"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSHAREHOLDERSEQUITYUnaudited" xlink:type="extended" id="i1ba6413bdf1747619cfe907e8b8728d8_CONSOLIDATEDSTATEMENTSOFCHANGESINSHAREHOLDERSEQUITYUnaudited">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_f3c5ce09-2dba-4738-acfd-1b35d35027a1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_us-gaap_SharesOutstanding_f3c5ce09-2dba-4738-acfd-1b35d35027a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_e966dd7f-da3b-437b-abf9-9691832e8d17" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_us-gaap_StockholdersEquity_e966dd7f-da3b-437b-abf9-9691832e8d17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_32c9b567-5501-44fb-b437-f5c505c46916" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_us-gaap_NetIncomeLoss_32c9b567-5501-44fb-b437-f5c505c46916" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_4e194e85-155f-487b-8067-74d1d71bfcfc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_4e194e85-155f-487b-8067-74d1d71bfcfc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_af909981-85b3-42a3-a8c1-add0d3d8ee32" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_af909981-85b3-42a3-a8c1-add0d3d8ee32" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_5587b50f-7d99-4fb9-98c8-4b1f50b33b36" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_5587b50f-7d99-4fb9-98c8-4b1f50b33b36" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_42875980-174c-4338-8f71-5a60531450fb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_42875980-174c-4338-8f71-5a60531450fb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_834f66ed-8f82-4f33-ba98-e9201bdc62ef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_834f66ed-8f82-4f33-ba98-e9201bdc62ef" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_APICShareBasedPaymentArrangementIncreaseForCostRecognitionInShares_6116ef73-8143-491e-8e35-e8c4264a8182" xlink:href="fsbc-20220930.xsd#fsbc_APICShareBasedPaymentArrangementIncreaseForCostRecognitionInShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_fsbc_APICShareBasedPaymentArrangementIncreaseForCostRecognitionInShares_6116ef73-8143-491e-8e35-e8c4264a8182" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_43eb671f-6596-4faa-9931-5aedef71c82f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_43eb671f-6596-4faa-9931-5aedef71c82f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_4ca459d6-0c01-4acd-9a7d-ca19460329c9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_4ca459d6-0c01-4acd-9a7d-ca19460329c9" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_e1fae45f-e581-420b-9510-484a811dbf55" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_e1fae45f-e581-420b-9510-484a811dbf55" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalOther_1ae55b0f-01e8-4f84-a0db-1ec7d048f694" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalOther_1ae55b0f-01e8-4f84-a0db-1ec7d048f694" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountingStandardsUpdateExtensibleList_44054b6f-0a4e-4bce-a98b-7320ee9ed3a6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountingStandardsUpdateExtensibleList"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_us-gaap_AccountingStandardsUpdateExtensibleList_44054b6f-0a4e-4bce-a98b-7320ee9ed3a6" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStock_5e809923-ac0f-478f-8645-589899c67873" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_us-gaap_DividendsCommonStock_5e809923-ac0f-478f-8645-589899c67873" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_69314570-8f7a-465e-a84d-41ada9b9b41e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_9747fc3e-7de5-463f-97da-2ae8e08b4321" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_38533212-ce75-463e-aeb0-4b8683c380c3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_92ee33ba-6522-407d-adbf-883e85d95d1e" xlink:to="loc_us-gaap_StatementTable_38533212-ce75-463e-aeb0-4b8683c380c3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_824ac7c1-e29a-4863-9253-d823821fe537" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_38533212-ce75-463e-aeb0-4b8683c380c3" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_824ac7c1-e29a-4863-9253-d823821fe537" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_824ac7c1-e29a-4863-9253-d823821fe537_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_824ac7c1-e29a-4863-9253-d823821fe537" xlink:to="loc_us-gaap_EquityComponentDomain_824ac7c1-e29a-4863-9253-d823821fe537_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_ce15ae62-efdb-4f57-8e42-037d98b87b4c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_824ac7c1-e29a-4863-9253-d823821fe537" xlink:to="loc_us-gaap_EquityComponentDomain_ce15ae62-efdb-4f57-8e42-037d98b87b4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_6243be2b-5829-49e9-b2cc-da0cc95f5e7f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_ce15ae62-efdb-4f57-8e42-037d98b87b4c" xlink:to="loc_us-gaap_CommonStockMember_6243be2b-5829-49e9-b2cc-da0cc95f5e7f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_4b23ffe5-3ad0-430b-a073-10d2da6945dd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_ce15ae62-efdb-4f57-8e42-037d98b87b4c" xlink:to="loc_us-gaap_RetainedEarningsMember_4b23ffe5-3ad0-430b-a073-10d2da6945dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_ba7f0029-0599-4b09-a148-6daaeec00d08" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_ce15ae62-efdb-4f57-8e42-037d98b87b4c" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_ba7f0029-0599-4b09-a148-6daaeec00d08" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_082957f8-79a4-47c4-8332-cae30b43133a" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_38533212-ce75-463e-aeb0-4b8683c380c3" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_082957f8-79a4-47c4-8332-cae30b43133a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_082957f8-79a4-47c4-8332-cae30b43133a_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_082957f8-79a4-47c4-8332-cae30b43133a" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_082957f8-79a4-47c4-8332-cae30b43133a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_4892b94c-6880-4cef-a81f-b49d6047c1eb" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_082957f8-79a4-47c4-8332-cae30b43133a" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_4892b94c-6880-4cef-a81f-b49d6047c1eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_7e0cf5cf-c40f-430f-ae30-3d917ddd3946" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_4892b94c-6880-4cef-a81f-b49d6047c1eb" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_7e0cf5cf-c40f-430f-ae30-3d917ddd3946" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusAxis_17d02802-a272-427f-802b-dd2de36a16ea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GranteeStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_38533212-ce75-463e-aeb0-4b8683c380c3" xlink:to="loc_us-gaap_GranteeStatusAxis_17d02802-a272-427f-802b-dd2de36a16ea" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_17d02802-a272-427f-802b-dd2de36a16ea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GranteeStatusAxis_17d02802-a272-427f-802b-dd2de36a16ea" xlink:to="loc_us-gaap_GranteeStatusDomain_17d02802-a272-427f-802b-dd2de36a16ea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_f3a8f32d-5f11-4c4c-ba4b-0e3f7f84a7b5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GranteeStatusAxis_17d02802-a272-427f-802b-dd2de36a16ea" xlink:to="loc_us-gaap_GranteeStatusDomain_f3a8f32d-5f11-4c4c-ba4b-0e3f7f84a7b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_7dcbcd9c-b0b7-43eb-915c-c8aa6fbac89a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedPaymentArrangementEmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_f3a8f32d-5f11-4c4c-ba4b-0e3f7f84a7b5" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_7dcbcd9c-b0b7-43eb-915c-c8aa6fbac89a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_b6a31868-fa5a-42a1-bb52-57f50a447b3a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedPaymentArrangementNonemployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_f3a8f32d-5f11-4c4c-ba4b-0e3f7f84a7b5" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_b6a31868-fa5a-42a1-bb52-57f50a447b3a" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/CONSOLIDATEDSTATEMENTSOFCASHFLOWSUnaudited" xlink:type="simple" xlink:href="fsbc-20220930.xsd#CONSOLIDATEDSTATEMENTSOFCASHFLOWSUnaudited"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/CONSOLIDATEDSTATEMENTSOFCASHFLOWSUnaudited" xlink:type="extended" id="idcac39b6ac9e4c9cb74cb9f45cca2fc2_CONSOLIDATEDSTATEMENTSOFCASHFLOWSUnaudited">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_513996a4-d6d4-4c7d-abbb-b4d16b912e57" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_60d949c8-3c0b-49ab-9564-d9fb81054fe3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_513996a4-d6d4-4c7d-abbb-b4d16b912e57" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_60d949c8-3c0b-49ab-9564-d9fb81054fe3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_82e25828-0aea-44aa-8724-fee4c0234eab" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_60d949c8-3c0b-49ab-9564-d9fb81054fe3" xlink:to="loc_us-gaap_NetIncomeLoss_82e25828-0aea-44aa-8724-fee4c0234eab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_513996a4-d6d4-4c7d-abbb-b4d16b912e57" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForLoanLeaseAndOtherLosses_75c212ee-66e4-4fa1-ac3e-f8ffbff7412b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProvisionForLoanLeaseAndOtherLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:to="loc_us-gaap_ProvisionForLoanLeaseAndOtherLosses_75c212ee-66e4-4fa1-ac3e-f8ffbff7412b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForOriginationAndPurchasesOfLoansHeldForSale_5609df39-ef2f-435b-a5f7-e4a382fe94ef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsForOriginationAndPurchasesOfLoansHeldForSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:to="loc_us-gaap_PaymentsForOriginationAndPurchasesOfLoansHeldForSale_5609df39-ef2f-435b-a5f7-e4a382fe94ef" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSalesOfLoansNet_9dabf2c7-8a5b-45ae-bcac-7cd76d035989" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GainLossOnSalesOfLoansNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:to="loc_us-gaap_GainLossOnSalesOfLoansNet_9dabf2c7-8a5b-45ae-bcac-7cd76d035989" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfLoansHeldForSale_d7c9aa6c-fe42-4958-b2e3-6010e831c857" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromSaleOfLoansHeldForSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:to="loc_us-gaap_ProceedsFromSaleOfLoansHeldForSale_d7c9aa6c-fe42-4958-b2e3-6010e831c857" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleRealizedGainLoss_31b7b800-4fb3-44f0-8efa-9e70dac7cd73" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleRealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleRealizedGainLoss_31b7b800-4fb3-44f0-8efa-9e70dac7cd73" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BankOwnedLifeInsuranceIncome_d470b124-c5d0-4881-9fc8-1576713d3bae" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BankOwnedLifeInsuranceIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:to="loc_us-gaap_BankOwnedLifeInsuranceIncome_d470b124-c5d0-4881-9fc8-1576713d3bae" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_c79af761-d170-4f9c-a7ae-be6955bfdc73" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:to="loc_us-gaap_ShareBasedCompensation_c79af761-d170-4f9c-a7ae-be6955bfdc73" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInDeferredLeasingFees_67a90b32-0849-49fb-860e-98838e910a5e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInDeferredLeasingFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:to="loc_us-gaap_IncreaseDecreaseInDeferredLeasingFees_67a90b32-0849-49fb-860e-98838e910a5e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_c966b3b0-45d6-4ae1-ad76-d3a17714fba6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:to="loc_us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_c966b3b0-45d6-4ae1-ad76-d3a17714fba6" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_506b6248-2baf-4c5a-a759-a52a5d35c430" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_506b6248-2baf-4c5a-a759-a52a5d35c430" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_427376e9-5391-4970-96a1-6520f34923a2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:to="loc_us-gaap_DepreciationAndAmortization_427376e9-5391-4970-96a1-6520f34923a2" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingLeaseLiability_f3e81c8c-3080-48a8-943a-27d055aec84c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingLeaseLiability_f3e81c8c-3080-48a8-943a-27d055aec84c" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_7f4d81e6-d8aa-4161-90e1-d0b54fab8683" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_7f4d81e6-d8aa-4161-90e1-d0b54fab8683" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_e78025dc-a473-4c46-a756-77f32ca85321" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_f0f8d726-ecdc-4da4-8d7f-d265beab66d7" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_e78025dc-a473-4c46-a756-77f32ca85321" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_1dfad61b-ec06-4d2e-b100-c7f9d8d24503" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_513996a4-d6d4-4c7d-abbb-b4d16b912e57" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_1dfad61b-ec06-4d2e-b100-c7f9d8d24503" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet_bf47d2dd-8193-4147-b450-89fa1c00f823" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_1dfad61b-ec06-4d2e-b100-c7f9d8d24503" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet_bf47d2dd-8193-4147-b450-89fa1c00f823" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInInterestPayableNet_a537ae68-1f33-4c6e-8e0f-1c977873aa89" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInInterestPayableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_1dfad61b-ec06-4d2e-b100-c7f9d8d24503" xlink:to="loc_us-gaap_IncreaseDecreaseInInterestPayableNet_a537ae68-1f33-4c6e-8e0f-1c977873aa89" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_feb77110-9719-4317-a82d-97f5a5ae1047" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_1dfad61b-ec06-4d2e-b100-c7f9d8d24503" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_feb77110-9719-4317-a82d-97f5a5ae1047" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d5d502c5-c79a-4093-a1ab-15047891829b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_513996a4-d6d4-4c7d-abbb-b4d16b912e57" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d5d502c5-c79a-4093-a1ab-15047891829b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_c7de66b8-24f6-4971-98ae-dbc2c4f65858" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d5d502c5-c79a-4093-a1ab-15047891829b" xlink:to="loc_us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_c7de66b8-24f6-4971-98ae-dbc2c4f65858" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities_1d7c3af5-29ed-4d46-96e9-86057623d33d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d5d502c5-c79a-4093-a1ab-15047891829b" xlink:to="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities_1d7c3af5-29ed-4d46-96e9-86057623d33d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt_e9317674-f609-41d7-899d-a66713eddc13" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d5d502c5-c79a-4093-a1ab-15047891829b" xlink:to="loc_us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt_e9317674-f609-41d7-899d-a66713eddc13" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromPaymentsForInInterestBearingDepositsInBanks_04c47377-29a6-478e-a34b-a1d9691fe94b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromPaymentsForInInterestBearingDepositsInBanks"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d5d502c5-c79a-4093-a1ab-15047891829b" xlink:to="loc_us-gaap_ProceedsFromPaymentsForInInterestBearingDepositsInBanks_04c47377-29a6-478e-a34b-a1d9691fe94b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_PaymentsForOriginationOfLoansNetOfProceedsFromRepayments_c6754724-ba4d-4991-bb6c-4094da7a7b76" xlink:href="fsbc-20220930.xsd#fsbc_PaymentsForOriginationOfLoansNetOfProceedsFromRepayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d5d502c5-c79a-4093-a1ab-15047891829b" xlink:to="loc_fsbc_PaymentsForOriginationOfLoansNetOfProceedsFromRepayments_c6754724-ba4d-4991-bb6c-4094da7a7b76" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_e927275b-4b51-44c6-adfd-34187cae44c1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d5d502c5-c79a-4093-a1ab-15047891829b" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_e927275b-4b51-44c6-adfd-34187cae44c1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromFederalHomeLoanBankStock_6ce1400e-5f42-472a-9d9b-cfe0bd255b75" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsForProceedsFromFederalHomeLoanBankStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d5d502c5-c79a-4093-a1ab-15047891829b" xlink:to="loc_us-gaap_PaymentsForProceedsFromFederalHomeLoanBankStock_6ce1400e-5f42-472a-9d9b-cfe0bd255b75" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireLifeInsurancePolicies_6e294184-9f72-4bb9-b7ff-5be7d61af31c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsToAcquireLifeInsurancePolicies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d5d502c5-c79a-4093-a1ab-15047891829b" xlink:to="loc_us-gaap_PaymentsToAcquireLifeInsurancePolicies_6e294184-9f72-4bb9-b7ff-5be7d61af31c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7f5c0f25-1167-4129-b43e-b062cbc33bd8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d5d502c5-c79a-4093-a1ab-15047891829b" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7f5c0f25-1167-4129-b43e-b062cbc33bd8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_110f9f1a-74d9-41b6-919f-004f05a6d64d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_513996a4-d6d4-4c7d-abbb-b4d16b912e57" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_110f9f1a-74d9-41b6-919f-004f05a6d64d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInDeposits_726d3649-9229-45b3-8728-238b69738284" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_110f9f1a-74d9-41b6-919f-004f05a6d64d" xlink:to="loc_us-gaap_IncreaseDecreaseInDeposits_726d3649-9229-45b3-8728-238b69738284" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_85d3b667-0652-42fe-84af-1a30c1327fe1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_110f9f1a-74d9-41b6-919f-004f05a6d64d" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_85d3b667-0652-42fe-84af-1a30c1327fe1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromFederalHomeLoanBankBorrowings_39a046b1-4c8d-4628-b2cb-190f61fd0bfb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromFederalHomeLoanBankBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_110f9f1a-74d9-41b6-919f-004f05a6d64d" xlink:to="loc_us-gaap_ProceedsFromFederalHomeLoanBankBorrowings_39a046b1-4c8d-4628-b2cb-190f61fd0bfb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividends_92d70c27-8be9-4944-a23d-f14da9de93db" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsOfDividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_110f9f1a-74d9-41b6-919f-004f05a6d64d" xlink:to="loc_us-gaap_PaymentsOfDividends_92d70c27-8be9-4944-a23d-f14da9de93db" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_38560a47-8994-4ebd-87a3-56192f545845" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromIssuanceOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_110f9f1a-74d9-41b6-919f-004f05a6d64d" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_38560a47-8994-4ebd-87a3-56192f545845" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDebtIssuanceCosts_2849d9bc-2f8a-470d-bd12-8e060545d104" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsOfDebtIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_110f9f1a-74d9-41b6-919f-004f05a6d64d" xlink:to="loc_us-gaap_PaymentsOfDebtIssuanceCosts_2849d9bc-2f8a-470d-bd12-8e060545d104" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_aacc47a7-536e-4224-ac7b-2e5c8bd69df2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_110f9f1a-74d9-41b6-919f-004f05a6d64d" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_aacc47a7-536e-4224-ac7b-2e5c8bd69df2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_6c0f04de-7543-496d-a31c-2416868ca265" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_513996a4-d6d4-4c7d-abbb-b4d16b912e57" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_6c0f04de-7543-496d-a31c-2416868ca265" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_1f54020f-2fb4-495e-8cc0-79f45c88ffe3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_513996a4-d6d4-4c7d-abbb-b4d16b912e57" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_1f54020f-2fb4-495e-8cc0-79f45c88ffe3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_37d26af4-453d-4d4b-8ba8-3563da0a4705" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_1bf35fc8-c928-4150-a07a-ee580be1e831" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SupplementalCashFlowInformationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_513996a4-d6d4-4c7d-abbb-b4d16b912e57" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_1bf35fc8-c928-4150-a07a-ee580be1e831" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaidNet_470789eb-edaa-4e9b-aa42-e7f2edb9c85f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_1bf35fc8-c928-4150-a07a-ee580be1e831" xlink:to="loc_us-gaap_InterestPaidNet_470789eb-edaa-4e9b-aa42-e7f2edb9c85f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_b9e6eac9-6841-4ba5-9f3b-a5aeee99ba78" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxesPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_1bf35fc8-c928-4150-a07a-ee580be1e831" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_b9e6eac9-6841-4ba5-9f3b-a5aeee99ba78" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9e1cfc72-90bc-466f-ad2c-ff5ab6c7897e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NoncashInvestingAndFinancingItemsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_513996a4-d6d4-4c7d-abbb-b4d16b912e57" xlink:to="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9e1cfc72-90bc-466f-ad2c-ff5ab6c7897e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_TransferFromLoansHeldForInvestmentToLoansHeldForSale_d56ea9c0-9f53-48a4-8587-3ca12190a4d8" xlink:href="fsbc-20220930.xsd#fsbc_TransferFromLoansHeldForInvestmentToLoansHeldForSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9e1cfc72-90bc-466f-ad2c-ff5ab6c7897e" xlink:to="loc_fsbc_TransferFromLoansHeldForInvestmentToLoansHeldForSale_d56ea9c0-9f53-48a4-8587-3ca12190a4d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnInvestments_bb2e3980-b130-47f2-8ed6-cd13787fd4e2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnrealizedGainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9e1cfc72-90bc-466f-ad2c-ff5ab6c7897e" xlink:to="loc_us-gaap_UnrealizedGainLossOnInvestments_bb2e3980-b130-47f2-8ed6-cd13787fd4e2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalLeaseObligationsIncurred_88f613f7-d2c2-47cb-871c-04f76d5fccf1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CapitalLeaseObligationsIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9e1cfc72-90bc-466f-ad2c-ff5ab6c7897e" xlink:to="loc_us-gaap_CapitalLeaseObligationsIncurred_88f613f7-d2c2-47cb-871c-04f76d5fccf1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_d28eb940-c58d-4c50-8a25-e9f26f926b69" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9e1cfc72-90bc-466f-ad2c-ff5ab6c7897e" xlink:to="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_d28eb940-c58d-4c50-8a25-e9f26f926b69" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_1dc7436a-adb0-4704-8b9e-14286baf3f96" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_9e1cfc72-90bc-466f-ad2c-ff5ab6c7897e" xlink:to="loc_us-gaap_StockholdersEquity_1dc7436a-adb0-4704-8b9e-14286baf3f96" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_6d453b8b-572b-4ae2-8808-e64ece2b5c89" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_513996a4-d6d4-4c7d-abbb-b4d16b912e57" xlink:to="loc_us-gaap_StatementTable_6d453b8b-572b-4ae2-8808-e64ece2b5c89" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusAxis_73690dbb-0526-4df2-8632-183ab07aa7fe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GranteeStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_6d453b8b-572b-4ae2-8808-e64ece2b5c89" xlink:to="loc_us-gaap_GranteeStatusAxis_73690dbb-0526-4df2-8632-183ab07aa7fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_73690dbb-0526-4df2-8632-183ab07aa7fe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GranteeStatusAxis_73690dbb-0526-4df2-8632-183ab07aa7fe" xlink:to="loc_us-gaap_GranteeStatusDomain_73690dbb-0526-4df2-8632-183ab07aa7fe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_7ad1c9da-99f8-4fda-9c85-7939a238f901" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GranteeStatusAxis_73690dbb-0526-4df2-8632-183ab07aa7fe" xlink:to="loc_us-gaap_GranteeStatusDomain_7ad1c9da-99f8-4fda-9c85-7939a238f901" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_98d35d38-dd4a-46fd-8570-706c32475326" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedPaymentArrangementEmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_7ad1c9da-99f8-4fda-9c85-7939a238f901" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_98d35d38-dd4a-46fd-8570-706c32475326" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_f1aa1f69-aa03-441f-9bd8-4b980ec9abd8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedPaymentArrangementNonemployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_7ad1c9da-99f8-4fda-9c85-7939a238f901" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_f1aa1f69-aa03-441f-9bd8-4b980ec9abd8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_e0050802-7371-4614-96a3-86b81ac84c8d" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_6d453b8b-572b-4ae2-8808-e64ece2b5c89" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_e0050802-7371-4614-96a3-86b81ac84c8d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_e0050802-7371-4614-96a3-86b81ac84c8d_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_e0050802-7371-4614-96a3-86b81ac84c8d" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_e0050802-7371-4614-96a3-86b81ac84c8d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_8eea56da-0106-40da-bc5d-0fe1aac9d88a" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_e0050802-7371-4614-96a3-86b81ac84c8d" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_8eea56da-0106-40da-bc5d-0fe1aac9d88a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_50ec8260-777d-43de-a7d6-b1a7aaf3951a" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_8eea56da-0106-40da-bc5d-0fe1aac9d88a" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_50ec8260-777d-43de-a7d6-b1a7aaf3951a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/BasisofPresentationNarrativeDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#BasisofPresentationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/BasisofPresentationNarrativeDetails" xlink:type="extended" id="i3792e016497440e9ad8a1ff8bada6325_BasisofPresentationNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockLineItems_ae07ee8a-fbcf-4648-9597-4efcda7fe1cb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsidiarySaleOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_CommonStockConvertibleSharesIssuable_d562da08-db57-4ee7-88c6-73978b942a2d" xlink:href="fsbc-20220930.xsd#fsbc_CommonStockConvertibleSharesIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_ae07ee8a-fbcf-4648-9597-4efcda7fe1cb" xlink:to="loc_fsbc_CommonStockConvertibleSharesIssuable_d562da08-db57-4ee7-88c6-73978b942a2d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_NumberOfBranchOffices_26ea9b72-b9c3-4db8-8e3c-9f6926245d06" xlink:href="fsbc-20220930.xsd#fsbc_NumberOfBranchOffices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_ae07ee8a-fbcf-4648-9597-4efcda7fe1cb" xlink:to="loc_fsbc_NumberOfBranchOffices_26ea9b72-b9c3-4db8-8e3c-9f6926245d06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_NumberOfLoanProductionOffices_ab4d697b-53b1-4d6b-b62c-cc753573777c" xlink:href="fsbc-20220930.xsd#fsbc_NumberOfLoanProductionOffices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_ae07ee8a-fbcf-4648-9597-4efcda7fe1cb" xlink:to="loc_fsbc_NumberOfLoanProductionOffices_ab4d697b-53b1-4d6b-b62c-cc753573777c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_bb82eec8-47ab-456d-98f7-2dcfb478b080" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_ae07ee8a-fbcf-4648-9597-4efcda7fe1cb" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_bb82eec8-47ab-456d-98f7-2dcfb478b080" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_f94d9293-c373-4962-a0d5-9c9538a21ef3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_ae07ee8a-fbcf-4648-9597-4efcda7fe1cb" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_f94d9293-c373-4962-a0d5-9c9538a21ef3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceInitialPublicOffering_2de460f7-1fd0-4c93-820e-9af08bdf8bed" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromIssuanceInitialPublicOffering"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_ae07ee8a-fbcf-4648-9597-4efcda7fe1cb" xlink:to="loc_us-gaap_ProceedsFromIssuanceInitialPublicOffering_2de460f7-1fd0-4c93-820e-9af08bdf8bed" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_119c213b-d977-4f8c-818b-5c15f3fecab6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_ae07ee8a-fbcf-4648-9597-4efcda7fe1cb" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_119c213b-d977-4f8c-818b-5c15f3fecab6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_caa09129-5931-48f8-96b7-f02d1679adc1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_ae07ee8a-fbcf-4648-9597-4efcda7fe1cb" xlink:to="loc_us-gaap_NumberOfReportableSegments_caa09129-5931-48f8-96b7-f02d1679adc1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_ProFormaTaxRate_5c4e3b2b-1a62-4393-b996-b890c08125e0" xlink:href="fsbc-20220930.xsd#fsbc_ProFormaTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_ae07ee8a-fbcf-4648-9597-4efcda7fe1cb" xlink:to="loc_fsbc_ProFormaTaxRate_5c4e3b2b-1a62-4393-b996-b890c08125e0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsAdjustmentOfDeferredTaxAssetLiability_99508435-42c2-4688-bd63-a54efd6ba01f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxExpenseBenefitContinuingOperationsAdjustmentOfDeferredTaxAssetLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_ae07ee8a-fbcf-4648-9597-4efcda7fe1cb" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsAdjustmentOfDeferredTaxAssetLiability_99508435-42c2-4688-bd63-a54efd6ba01f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_6f1cce5c-3af4-4c95-a789-f008b7195407" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_ae07ee8a-fbcf-4648-9597-4efcda7fe1cb" xlink:to="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_6f1cce5c-3af4-4c95-a789-f008b7195407" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_ca2b9a2b-0583-4bd1-b478-d94695563330" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_6f1cce5c-3af4-4c95-a789-f008b7195407" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_ca2b9a2b-0583-4bd1-b478-d94695563330" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_ca2b9a2b-0583-4bd1-b478-d94695563330_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_ca2b9a2b-0583-4bd1-b478-d94695563330" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_ca2b9a2b-0583-4bd1-b478-d94695563330_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_a1402240-502a-47a2-920d-a84da5e7891c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_ca2b9a2b-0583-4bd1-b478-d94695563330" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_a1402240-502a-47a2-920d-a84da5e7891c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IPOMember_e5d852b7-41a1-4ef4-846a-8d3104920542" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IPOMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_a1402240-502a-47a2-920d-a84da5e7891c" xlink:to="loc_us-gaap_IPOMember_e5d852b7-41a1-4ef4-846a-8d3104920542" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OverAllotmentOptionMember_edb03232-810e-49f5-9706-b2156522e1e8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OverAllotmentOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_a1402240-502a-47a2-920d-a84da5e7891c" xlink:to="loc_us-gaap_OverAllotmentOptionMember_edb03232-810e-49f5-9706-b2156522e1e8" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/FairValueofAssetsandLiabilitiesFairValueofAssetsandLiabilitiesMeasuredonRecurringBasisDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#FairValueofAssetsandLiabilitiesFairValueofAssetsandLiabilitiesMeasuredonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/FairValueofAssetsandLiabilitiesFairValueofAssetsandLiabilitiesMeasuredonRecurringBasisDetails" xlink:type="extended" id="i9851c3697ce54b0b833a815a82793d30_FairValueofAssetsandLiabilitiesFairValueofAssetsandLiabilitiesMeasuredonRecurringBasisDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f7c5c5c6-fbf6-4a6c-a667-063437c051b5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_a03cba9a-4925-4b74-99e5-953b8a1c3f1f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f7c5c5c6-fbf6-4a6c-a667-063437c051b5" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_a03cba9a-4925-4b74-99e5-953b8a1c3f1f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_6996a5a0-a953-4098-92d2-90432bcdb171" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f7c5c5c6-fbf6-4a6c-a667-063437c051b5" xlink:to="loc_us-gaap_DerivativeAssets_6996a5a0-a953-4098-92d2-90432bcdb171" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_4997f010-cd8b-4e92-9676-ae08a0f65269" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f7c5c5c6-fbf6-4a6c-a667-063437c051b5" xlink:to="loc_us-gaap_DerivativeLiabilities_4997f010-cd8b-4e92-9676-ae08a0f65269" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d69aad51-51a9-4946-a83a-b2471ed3420c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f7c5c5c6-fbf6-4a6c-a667-063437c051b5" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d69aad51-51a9-4946-a83a-b2471ed3420c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_8809bc41-d081-40ff-b036-222c21bd39ee" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d69aad51-51a9-4946-a83a-b2471ed3420c" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_8809bc41-d081-40ff-b036-222c21bd39ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_8809bc41-d081-40ff-b036-222c21bd39ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_8809bc41-d081-40ff-b036-222c21bd39ee" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_8809bc41-d081-40ff-b036-222c21bd39ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_4c121cac-f488-4fc6-809d-c20dd06a1a45" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_8809bc41-d081-40ff-b036-222c21bd39ee" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_4c121cac-f488-4fc6-809d-c20dd06a1a45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsTotalMember_a6b69d58-3290-450f-a531-c89ee594de15" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsTotalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_4c121cac-f488-4fc6-809d-c20dd06a1a45" xlink:to="loc_us-gaap_AssetsTotalMember_a6b69d58-3290-450f-a531-c89ee594de15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesTotalMember_ac99b1e5-11b2-40f8-b739-b0982b385fda" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesTotalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_4c121cac-f488-4fc6-809d-c20dd06a1a45" xlink:to="loc_us-gaap_LiabilitiesTotalMember_ac99b1e5-11b2-40f8-b739-b0982b385fda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_eba6f33d-293b-4d99-bb60-b2c6300e67b6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d69aad51-51a9-4946-a83a-b2471ed3420c" xlink:to="loc_us-gaap_FinancialInstrumentAxis_eba6f33d-293b-4d99-bb60-b2c6300e67b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_eba6f33d-293b-4d99-bb60-b2c6300e67b6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_eba6f33d-293b-4d99-bb60-b2c6300e67b6" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_eba6f33d-293b-4d99-bb60-b2c6300e67b6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_efd38e23-b245-4580-a2be-d746858cf984" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_eba6f33d-293b-4d99-bb60-b2c6300e67b6" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_efd38e23-b245-4580-a2be-d746858cf984" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableforsaleSecuritiesMember_5f61ddd7-aa3b-40c6-bee7-f47d0276a0ac" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableforsaleSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_efd38e23-b245-4580-a2be-d746858cf984" xlink:to="loc_us-gaap_AvailableforsaleSecuritiesMember_5f61ddd7-aa3b-40c6-bee7-f47d0276a0ac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_9d97353f-e8b6-4a10-818b-e0e670e45e43" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_efd38e23-b245-4580-a2be-d746858cf984" xlink:to="loc_us-gaap_InterestRateSwapMember_9d97353f-e8b6-4a10-818b-e0e670e45e43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_c61e33c2-1b19-40f2-aeb8-c2eeb620fc21" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d69aad51-51a9-4946-a83a-b2471ed3420c" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_c61e33c2-1b19-40f2-aeb8-c2eeb620fc21" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_c61e33c2-1b19-40f2-aeb8-c2eeb620fc21_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_c61e33c2-1b19-40f2-aeb8-c2eeb620fc21" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_c61e33c2-1b19-40f2-aeb8-c2eeb620fc21_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_4135075e-4b8a-41ef-b983-a57585aa826e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_c61e33c2-1b19-40f2-aeb8-c2eeb620fc21" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_4135075e-4b8a-41ef-b983-a57585aa826e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_c96b3dee-2ec1-4b99-8a0a-eb6e1ccb2984" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_4135075e-4b8a-41ef-b983-a57585aa826e" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_c96b3dee-2ec1-4b99-8a0a-eb6e1ccb2984" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_24226e07-5f75-4b87-a18f-f6505b1e2dca" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d69aad51-51a9-4946-a83a-b2471ed3420c" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_24226e07-5f75-4b87-a18f-f6505b1e2dca" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_24226e07-5f75-4b87-a18f-f6505b1e2dca_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_24226e07-5f75-4b87-a18f-f6505b1e2dca" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_24226e07-5f75-4b87-a18f-f6505b1e2dca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d6031afd-85e3-4483-a76c-365033e99aff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_24226e07-5f75-4b87-a18f-f6505b1e2dca" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d6031afd-85e3-4483-a76c-365033e99aff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_7744f41a-9490-421a-93a7-f5331f00404f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d6031afd-85e3-4483-a76c-365033e99aff" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_7744f41a-9490-421a-93a7-f5331f00404f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_2022cc52-885e-4dfe-a037-fdc25f0a6136" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d6031afd-85e3-4483-a76c-365033e99aff" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_2022cc52-885e-4dfe-a037-fdc25f0a6136" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_e9807345-1bc4-432f-af61-78a860e75bf2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d6031afd-85e3-4483-a76c-365033e99aff" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_e9807345-1bc4-432f-af61-78a860e75bf2" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/FairValueofAssetsandLiabilitiesFairValueEstimatesforFinancialInstrumentsbyBalanceSheetGroupingDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#FairValueofAssetsandLiabilitiesFairValueEstimatesforFinancialInstrumentsbyBalanceSheetGroupingDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/FairValueofAssetsandLiabilitiesFairValueEstimatesforFinancialInstrumentsbyBalanceSheetGroupingDetails" xlink:type="extended" id="i29d1ae9ff65040af8898acb7ce8bb6e0_FairValueofAssetsandLiabilitiesFairValueEstimatesforFinancialInstrumentsbyBalanceSheetGroupingDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_bf92af77-4420-4dd0-9397-4e690a2895ce" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FinancialAssetsRecordedAtAmortizedCostAbstract_da4c79bd-8cf9-40d9-a3c4-9ba8633166eb" xlink:href="fsbc-20220930.xsd#fsbc_FinancialAssetsRecordedAtAmortizedCostAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_bf92af77-4420-4dd0-9397-4e690a2895ce" xlink:to="loc_fsbc_FinancialAssetsRecordedAtAmortizedCostAbstract_da4c79bd-8cf9-40d9-a3c4-9ba8633166eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_24bd41e4-18ff-470d-8987-beb9316837ab" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsbc_FinancialAssetsRecordedAtAmortizedCostAbstract_da4c79bd-8cf9-40d9-a3c4-9ba8633166eb" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_24bd41e4-18ff-470d-8987-beb9316837ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_TimeDepositAtFairValueDisclosure_73090f17-b52e-4dca-a970-0fea5d56599d" xlink:href="fsbc-20220930.xsd#fsbc_TimeDepositAtFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsbc_FinancialAssetsRecordedAtAmortizedCostAbstract_da4c79bd-8cf9-40d9-a3c4-9ba8633166eb" xlink:to="loc_fsbc_TimeDepositAtFairValueDisclosure_73090f17-b52e-4dca-a970-0fea5d56599d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_71f35663-b8c5-4120-bf62-61368f354530" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsbc_FinancialAssetsRecordedAtAmortizedCostAbstract_da4c79bd-8cf9-40d9-a3c4-9ba8633166eb" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_71f35663-b8c5-4120-bf62-61368f354530" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesFairValue_ee77e190-233e-428b-9bf5-70367901c517" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsbc_FinancialAssetsRecordedAtAmortizedCostAbstract_da4c79bd-8cf9-40d9-a3c4-9ba8633166eb" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesFairValue_ee77e190-233e-428b-9bf5-70367901c517" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansHeldForSaleFairValueDisclosure_3549f936-83e3-469c-84a4-39628b8277fa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansHeldForSaleFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsbc_FinancialAssetsRecordedAtAmortizedCostAbstract_da4c79bd-8cf9-40d9-a3c4-9ba8633166eb" xlink:to="loc_us-gaap_LoansHeldForSaleFairValueDisclosure_3549f936-83e3-469c-84a4-39628b8277fa" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableFairValueDisclosure_400aaef2-94a9-4d2f-84d1-354c7855ab30" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansReceivableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsbc_FinancialAssetsRecordedAtAmortizedCostAbstract_da4c79bd-8cf9-40d9-a3c4-9ba8633166eb" xlink:to="loc_us-gaap_LoansReceivableFairValueDisclosure_400aaef2-94a9-4d2f-84d1-354c7855ab30" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentInFederalHomeLoanBankStockFairValueDisclosure_9b0bb15a-febe-477f-89de-cea3ec2850da" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InvestmentInFederalHomeLoanBankStockFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsbc_FinancialAssetsRecordedAtAmortizedCostAbstract_da4c79bd-8cf9-40d9-a3c4-9ba8633166eb" xlink:to="loc_us-gaap_InvestmentInFederalHomeLoanBankStockFairValueDisclosure_9b0bb15a-febe-477f-89de-cea3ec2850da" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableFairValueDisclosure_a02c7ab5-6d21-4201-b171-740370b5e1b2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountsReceivableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsbc_FinancialAssetsRecordedAtAmortizedCostAbstract_da4c79bd-8cf9-40d9-a3c4-9ba8633166eb" xlink:to="loc_us-gaap_AccountsReceivableFairValueDisclosure_a02c7ab5-6d21-4201-b171-740370b5e1b2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_bbce90dd-d395-436d-93ef-5692f8767cd3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsbc_FinancialAssetsRecordedAtAmortizedCostAbstract_da4c79bd-8cf9-40d9-a3c4-9ba8633166eb" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_bbce90dd-d395-436d-93ef-5692f8767cd3" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FinancialLiabilitiesRecordedAtAmortizedCostAbstract_67004a51-a60f-4145-b064-8090a06c05aa" xlink:href="fsbc-20220930.xsd#fsbc_FinancialLiabilitiesRecordedAtAmortizedCostAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_bf92af77-4420-4dd0-9397-4e690a2895ce" xlink:to="loc_fsbc_FinancialLiabilitiesRecordedAtAmortizedCostAbstract_67004a51-a60f-4145-b064-8090a06c05aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepositsFairValueDisclosure_cfe12802-e8ff-4121-afda-59d15a051fd7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DepositsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsbc_FinancialLiabilitiesRecordedAtAmortizedCostAbstract_67004a51-a60f-4145-b064-8090a06c05aa" xlink:to="loc_us-gaap_DepositsFairValueDisclosure_cfe12802-e8ff-4121-afda-59d15a051fd7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableFairValueDisclosure_e7d6eb1f-08f3-4817-8874-6c2fc9281fa6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountsPayableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsbc_FinancialLiabilitiesRecordedAtAmortizedCostAbstract_67004a51-a60f-4145-b064-8090a06c05aa" xlink:to="loc_us-gaap_AccountsPayableFairValueDisclosure_e7d6eb1f-08f3-4817-8874-6c2fc9281fa6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_835375e1-08b9-48a2-bbf0-058ae65dd34f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsbc_FinancialLiabilitiesRecordedAtAmortizedCostAbstract_67004a51-a60f-4145-b064-8090a06c05aa" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_835375e1-08b9-48a2-bbf0-058ae65dd34f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations_426315db-a75d-4129-8a23-12214df48645" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsbc_FinancialLiabilitiesRecordedAtAmortizedCostAbstract_67004a51-a60f-4145-b064-8090a06c05aa" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations_426315db-a75d-4129-8a23-12214df48645" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_5f2734a8-0dc8-4bde-ab1f-aad921d9d140" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_bf92af77-4420-4dd0-9397-4e690a2895ce" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_5f2734a8-0dc8-4bde-ab1f-aad921d9d140" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_7afbdc80-6c87-4113-ae14-030e40ecfd06" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_5f2734a8-0dc8-4bde-ab1f-aad921d9d140" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_7afbdc80-6c87-4113-ae14-030e40ecfd06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_7afbdc80-6c87-4113-ae14-030e40ecfd06_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_7afbdc80-6c87-4113-ae14-030e40ecfd06" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_7afbdc80-6c87-4113-ae14-030e40ecfd06_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_889b19f6-b6f9-40c5-84be-afbe5ae6611d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_7afbdc80-6c87-4113-ae14-030e40ecfd06" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_889b19f6-b6f9-40c5-84be-afbe5ae6611d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_c96aaf28-635c-4c4c-96a9-899f1df9ff67" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_889b19f6-b6f9-40c5-84be-afbe5ae6611d" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_c96aaf28-635c-4c4c-96a9-899f1df9ff67" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_1ad1faec-909a-4ac2-8590-fd92f19ec0a8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_889b19f6-b6f9-40c5-84be-afbe5ae6611d" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_1ad1faec-909a-4ac2-8590-fd92f19ec0a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_83bb5a40-2b6c-44ce-a7b1-343cb0f57b38" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_889b19f6-b6f9-40c5-84be-afbe5ae6611d" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_83bb5a40-2b6c-44ce-a7b1-343cb0f57b38" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_fa868b98-efa1-419e-ad38-f86e280b5ead" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_5f2734a8-0dc8-4bde-ab1f-aad921d9d140" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_fa868b98-efa1-419e-ad38-f86e280b5ead" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_fa868b98-efa1-419e-ad38-f86e280b5ead_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_fa868b98-efa1-419e-ad38-f86e280b5ead" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_fa868b98-efa1-419e-ad38-f86e280b5ead_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_358e5e2d-5932-4c3f-80eb-da9a828b0c63" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_fa868b98-efa1-419e-ad38-f86e280b5ead" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_358e5e2d-5932-4c3f-80eb-da9a828b0c63" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_801a7b32-9f38-4092-b170-49e036a33ad1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_358e5e2d-5932-4c3f-80eb-da9a828b0c63" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_801a7b32-9f38-4092-b170-49e036a33ad1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_45c5f5ae-2616-4645-bcd8-30402da6f38b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_358e5e2d-5932-4c3f-80eb-da9a828b0c63" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_45c5f5ae-2616-4645-bcd8-30402da6f38b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_db70708b-95ad-4c26-89bd-ce35d6b4ff3e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_358e5e2d-5932-4c3f-80eb-da9a828b0c63" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_db70708b-95ad-4c26-89bd-ce35d6b4ff3e" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/InvestmentSecuritiesAmortizedCostandFairValueofSecuritiesHeldtomaturityDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#InvestmentSecuritiesAmortizedCostandFairValueofSecuritiesHeldtomaturityDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/InvestmentSecuritiesAmortizedCostandFairValueofSecuritiesHeldtomaturityDetails" xlink:type="extended" id="i1f21135e070540f0a6e5f9db79d26893_InvestmentSecuritiesAmortizedCostandFairValueofSecuritiesHeldtomaturityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_b281f8d6-c1dd-494d-9d39-266239c7cd98" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecurities_4b0b41eb-96b4-46b1-97f5-04912e531baa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_b281f8d6-c1dd-494d-9d39-266239c7cd98" xlink:to="loc_us-gaap_HeldToMaturitySecurities_4b0b41eb-96b4-46b1-97f5-04912e531baa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain_a0064234-1832-44f2-8b10-813fa3df5cb3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_b281f8d6-c1dd-494d-9d39-266239c7cd98" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain_a0064234-1832-44f2-8b10-813fa3df5cb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss_44901f8c-55f2-4d09-aa2b-f2d006afc087" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_b281f8d6-c1dd-494d-9d39-266239c7cd98" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss_44901f8c-55f2-4d09-aa2b-f2d006afc087" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesFairValue_e12f7000-917e-4970-81c5-672fea20b50c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_b281f8d6-c1dd-494d-9d39-266239c7cd98" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesFairValue_e12f7000-917e-4970-81c5-672fea20b50c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_7616d7bc-5cec-4e57-9530-949da251065a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_b281f8d6-c1dd-494d-9d39-266239c7cd98" xlink:to="loc_us-gaap_MarketableSecuritiesTable_7616d7bc-5cec-4e57-9530-949da251065a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_78a60b43-2160-4a86-85f0-84a740576c29" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_7616d7bc-5cec-4e57-9530-949da251065a" xlink:to="loc_us-gaap_FinancialInstrumentAxis_78a60b43-2160-4a86-85f0-84a740576c29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_78a60b43-2160-4a86-85f0-84a740576c29_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_78a60b43-2160-4a86-85f0-84a740576c29" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_78a60b43-2160-4a86-85f0-84a740576c29_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_51e6362c-422d-4a09-8f55-0d17da565502" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_78a60b43-2160-4a86-85f0-84a740576c29" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_51e6362c-422d-4a09-8f55-0d17da565502" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_c88fb0bd-d0d4-41d7-8241-6aff5ce8d896" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_51e6362c-422d-4a09-8f55-0d17da565502" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_c88fb0bd-d0d4-41d7-8241-6aff5ce8d896" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/InvestmentSecuritiesAmortizedCostandFairValueofSecuritiesAvailableforsaleDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#InvestmentSecuritiesAmortizedCostandFairValueofSecuritiesAvailableforsaleDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/InvestmentSecuritiesAmortizedCostandFairValueofSecuritiesAvailableforsaleDetails" xlink:type="extended" id="id873cf45dd27432f87ca8885381b3173_InvestmentSecuritiesAmortizedCostandFairValueofSecuritiesAvailableforsaleDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_d569fc55-150f-41f0-8f4a-adb17157d2e2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_48a39a74-2965-47e8-8864-0f9117a794fe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_d569fc55-150f-41f0-8f4a-adb17157d2e2" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_48a39a74-2965-47e8-8864-0f9117a794fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_dfe3613e-1c3f-422a-8f53-fe0c415dbe5d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_d569fc55-150f-41f0-8f4a-adb17157d2e2" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_dfe3613e-1c3f-422a-8f53-fe0c415dbe5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_f916ec2b-94c4-4300-9e53-1ea1d0fb66f1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_d569fc55-150f-41f0-8f4a-adb17157d2e2" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_f916ec2b-94c4-4300-9e53-1ea1d0fb66f1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_c3ff2e0a-6826-47e1-8308-f0563e13888d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_d569fc55-150f-41f0-8f4a-adb17157d2e2" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_c3ff2e0a-6826-47e1-8308-f0563e13888d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_e7088739-c177-40a8-a338-2da29eccaa94" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_d569fc55-150f-41f0-8f4a-adb17157d2e2" xlink:to="loc_us-gaap_MarketableSecuritiesTable_e7088739-c177-40a8-a338-2da29eccaa94" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_0eb696ea-0bb5-4d25-9a71-6dfb3de32d11" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_e7088739-c177-40a8-a338-2da29eccaa94" xlink:to="loc_us-gaap_FinancialInstrumentAxis_0eb696ea-0bb5-4d25-9a71-6dfb3de32d11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0eb696ea-0bb5-4d25-9a71-6dfb3de32d11_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_0eb696ea-0bb5-4d25-9a71-6dfb3de32d11" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0eb696ea-0bb5-4d25-9a71-6dfb3de32d11_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0f5a4d65-ed78-4df5-a5db-397a99a1cf9d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_0eb696ea-0bb5-4d25-9a71-6dfb3de32d11" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0f5a4d65-ed78-4df5-a5db-397a99a1cf9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_cdc33876-0a93-4a71-93ec-fe416268bd47" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0f5a4d65-ed78-4df5-a5db-397a99a1cf9d" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_cdc33876-0a93-4a71-93ec-fe416268bd47" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember_a4337fff-89d8-41e2-a352-8707e5013f15" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0f5a4d65-ed78-4df5-a5db-397a99a1cf9d" xlink:to="loc_us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember_a4337fff-89d8-41e2-a352-8707e5013f15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_37e4548f-8cdc-4d73-bf2d-b5b4bcb9b9fc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0f5a4d65-ed78-4df5-a5db-397a99a1cf9d" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_37e4548f-8cdc-4d73-bf2d-b5b4bcb9b9fc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralizedDebtObligationsMember_c862cf3b-cb87-4cd1-b981-62e9d552041f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CollateralizedDebtObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0f5a4d65-ed78-4df5-a5db-397a99a1cf9d" xlink:to="loc_us-gaap_CollateralizedDebtObligationsMember_c862cf3b-cb87-4cd1-b981-62e9d552041f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_8bd72ae6-8cbf-402f-a6f3-9caa6e09bebb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0f5a4d65-ed78-4df5-a5db-397a99a1cf9d" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_8bd72ae6-8cbf-402f-a6f3-9caa6e09bebb" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/InvestmentSecuritiesAmortizedCostandFairValueofInvestmentDebtSecuritiesbyContractualMaturityDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#InvestmentSecuritiesAmortizedCostandFairValueofInvestmentDebtSecuritiesbyContractualMaturityDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/InvestmentSecuritiesAmortizedCostandFairValueofInvestmentDebtSecuritiesbyContractualMaturityDetails" xlink:type="extended" id="i6bd376f27b124feba8850e611cc566bc_InvestmentSecuritiesAmortizedCostandFairValueofInvestmentDebtSecuritiesbyContractualMaturityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_658d8515-e6c5-4669-a105-2035080c5f67" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAbstract_e4cf2464-c269-413b-8255-6ed0f6432f56" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_658d8515-e6c5-4669-a105-2035080c5f67" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAbstract_e4cf2464-c269-413b-8255-6ed0f6432f56" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract_7b7d1176-f9a3-4fcf-a5f8-92b72d2d67b1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAbstract_e4cf2464-c269-413b-8255-6ed0f6432f56" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract_7b7d1176-f9a3-4fcf-a5f8-92b72d2d67b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount_3d1b3d47-7843-4a67-be21-22a8f5478c02" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract_7b7d1176-f9a3-4fcf-a5f8-92b72d2d67b1" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount_3d1b3d47-7843-4a67-be21-22a8f5478c02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsNetCarryingAmount_132a144c-ad98-496c-a7df-efdc23ca70ee" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsNetCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract_7b7d1176-f9a3-4fcf-a5f8-92b72d2d67b1" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsNetCarryingAmount_132a144c-ad98-496c-a7df-efdc23ca70ee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsNetCarryingAmount_fa7545e4-669f-4421-862f-568b70571b64" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsNetCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract_7b7d1176-f9a3-4fcf-a5f8-92b72d2d67b1" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsNetCarryingAmount_fa7545e4-669f-4421-862f-568b70571b64" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsNetCarryingAmount_ca3d4c4d-7c86-4446-aafb-88542d7ef34a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsNetCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract_7b7d1176-f9a3-4fcf-a5f8-92b72d2d67b1" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsNetCarryingAmount_ca3d4c4d-7c86-4446-aafb-88542d7ef34a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateFairValueAbstract_59fe68b0-d944-46c9-bcf5-4a87758c2980" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateFairValueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAbstract_e4cf2464-c269-413b-8255-6ed0f6432f56" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateFairValueAbstract_59fe68b0-d944-46c9-bcf5-4a87758c2980" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue_6cba0df7-41ea-45d3-abdf-ce055a08a22f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateFairValueAbstract_59fe68b0-d944-46c9-bcf5-4a87758c2980" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue_6cba0df7-41ea-45d3-abdf-ce055a08a22f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_822ff8a9-f3e2-453e-bb10-c4421e744d11" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateFairValueAbstract_59fe68b0-d944-46c9-bcf5-4a87758c2980" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_822ff8a9-f3e2-453e-bb10-c4421e744d11" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_b881a01a-6a36-4a08-afda-8b7ccc714c46" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateFairValueAbstract_59fe68b0-d944-46c9-bcf5-4a87758c2980" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_b881a01a-6a36-4a08-afda-8b7ccc714c46" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsFairValue_99ff6962-5888-4276-94a1-fc22a44d69de" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateFairValueAbstract_59fe68b0-d944-46c9-bcf5-4a87758c2980" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsFairValue_99ff6962-5888-4276-94a1-fc22a44d69de" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAbstract_cd0b493f-b084-4e40-b59b-ac3a9be58fba" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_658d8515-e6c5-4669-a105-2035080c5f67" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAbstract_cd0b493f-b084-4e40-b59b-ac3a9be58fba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract_bf3b0145-cecc-4912-bb59-56aa4e03b15f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAbstract_cd0b493f-b084-4e40-b59b-ac3a9be58fba" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract_bf3b0145-cecc-4912-bb59-56aa4e03b15f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost_02f92db5-36b1-478a-be6f-620b81c5e5a7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract_bf3b0145-cecc-4912-bb59-56aa4e03b15f" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost_02f92db5-36b1-478a-be6f-620b81c5e5a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost_e0d20a01-56df-4287-9566-a49b198944e6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract_bf3b0145-cecc-4912-bb59-56aa4e03b15f" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost_e0d20a01-56df-4287-9566-a49b198944e6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost_799c0843-eea4-458c-8f58-79b29ef5fb61" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract_bf3b0145-cecc-4912-bb59-56aa4e03b15f" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost_799c0843-eea4-458c-8f58-79b29ef5fb61" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost_e1e1b4e9-6c01-41aa-95ae-9b7e15f57825" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract_bf3b0145-cecc-4912-bb59-56aa4e03b15f" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost_e1e1b4e9-6c01-41aa-95ae-9b7e15f57825" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAbstract_65d8c8c0-d1b7-4873-8141-a3b3710a062e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAbstract_cd0b493f-b084-4e40-b59b-ac3a9be58fba" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAbstract_65d8c8c0-d1b7-4873-8141-a3b3710a062e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_a6362ada-10b7-41fd-87e4-b2980f4cbdd0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAbstract_65d8c8c0-d1b7-4873-8141-a3b3710a062e" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_a6362ada-10b7-41fd-87e4-b2980f4cbdd0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_dd9507b5-34f0-4b95-a766-5e43f22089b4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAbstract_65d8c8c0-d1b7-4873-8141-a3b3710a062e" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_dd9507b5-34f0-4b95-a766-5e43f22089b4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_68e9f554-9728-4f4f-bcc9-4a4988f90108" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAbstract_65d8c8c0-d1b7-4873-8141-a3b3710a062e" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_68e9f554-9728-4f4f-bcc9-4a4988f90108" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue_63740e96-68a0-4eba-8099-cb87a634b68c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAbstract_65d8c8c0-d1b7-4873-8141-a3b3710a062e" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue_63740e96-68a0-4eba-8099-cb87a634b68c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecurities_87d0c6b9-dfb0-4900-a308-2ae92e09caa6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_658d8515-e6c5-4669-a105-2035080c5f67" xlink:to="loc_us-gaap_HeldToMaturitySecurities_87d0c6b9-dfb0-4900-a308-2ae92e09caa6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesFairValue_b1e6f39d-64cb-4863-946f-28bd882e9d9a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecuritiesFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_658d8515-e6c5-4669-a105-2035080c5f67" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesFairValue_b1e6f39d-64cb-4863-946f-28bd882e9d9a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_58c24bc2-6cde-4e19-a7e1-4b5b9a69bcdd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_658d8515-e6c5-4669-a105-2035080c5f67" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_58c24bc2-6cde-4e19-a7e1-4b5b9a69bcdd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_0a172a7e-d801-4a0f-86e7-7442294d97ab" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_658d8515-e6c5-4669-a105-2035080c5f67" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_0a172a7e-d801-4a0f-86e7-7442294d97ab" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_6afa5eab-0652-4eab-b16d-de746fb3f113" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_658d8515-e6c5-4669-a105-2035080c5f67" xlink:to="loc_us-gaap_MarketableSecuritiesTable_6afa5eab-0652-4eab-b16d-de746fb3f113" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_5d23ddb4-e6f7-40e6-ae15-a4e547547e31" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_6afa5eab-0652-4eab-b16d-de746fb3f113" xlink:to="loc_us-gaap_FinancialInstrumentAxis_5d23ddb4-e6f7-40e6-ae15-a4e547547e31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_5d23ddb4-e6f7-40e6-ae15-a4e547547e31_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_5d23ddb4-e6f7-40e6-ae15-a4e547547e31" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_5d23ddb4-e6f7-40e6-ae15-a4e547547e31_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a284dcfa-e336-418e-9fe3-7f25f11003b0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_5d23ddb4-e6f7-40e6-ae15-a4e547547e31" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a284dcfa-e336-418e-9fe3-7f25f11003b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_b9615e1f-8360-4e95-b99d-14326e95f114" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a284dcfa-e336-418e-9fe3-7f25f11003b0" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_b9615e1f-8360-4e95-b99d-14326e95f114" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember_a42a992f-40f7-4277-83f6-a8d1ab68683e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a284dcfa-e336-418e-9fe3-7f25f11003b0" xlink:to="loc_us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember_a42a992f-40f7-4277-83f6-a8d1ab68683e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralizedDebtObligationsMember_40e658f1-be73-4c72-8b0f-b20e5fc53d65" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CollateralizedDebtObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a284dcfa-e336-418e-9fe3-7f25f11003b0" xlink:to="loc_us-gaap_CollateralizedDebtObligationsMember_40e658f1-be73-4c72-8b0f-b20e5fc53d65" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_a73b727f-c7cf-4652-ace4-1a85a0b5b425" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a284dcfa-e336-418e-9fe3-7f25f11003b0" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_a73b727f-c7cf-4652-ace4-1a85a0b5b425" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/InvestmentSecuritiesPledgedInvestmentSecuritiesDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#InvestmentSecuritiesPledgedInvestmentSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/InvestmentSecuritiesPledgedInvestmentSecuritiesDetails" xlink:type="extended" id="i5dca01d154f1493caaea0c33fdf4f6a5_InvestmentSecuritiesPledgedInvestmentSecuritiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_7ae4d7a7-fdd1-4e8a-8b6b-2d905e5b8294" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PledgedAssetsSeparatelyReportedMortgageRelatedSecuritiesAvailableForSaleOrHeldForInvestment_3f710177-15a8-47d1-9238-b36510d0a3b3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PledgedAssetsSeparatelyReportedMortgageRelatedSecuritiesAvailableForSaleOrHeldForInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_7ae4d7a7-fdd1-4e8a-8b6b-2d905e5b8294" xlink:to="loc_us-gaap_PledgedAssetsSeparatelyReportedMortgageRelatedSecuritiesAvailableForSaleOrHeldForInvestment_3f710177-15a8-47d1-9238-b36510d0a3b3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_4625fb40-2f28-477f-ba10-5f8103d996d6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_7ae4d7a7-fdd1-4e8a-8b6b-2d905e5b8294" xlink:to="loc_us-gaap_MarketableSecuritiesTable_4625fb40-2f28-477f-ba10-5f8103d996d6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_0aabad08-ee57-4a66-b006-a42786ba06bf" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_4625fb40-2f28-477f-ba10-5f8103d996d6" xlink:to="loc_srt_StatementGeographicalAxis_0aabad08-ee57-4a66-b006-a42786ba06bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_0aabad08-ee57-4a66-b006-a42786ba06bf_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_0aabad08-ee57-4a66-b006-a42786ba06bf" xlink:to="loc_srt_SegmentGeographicalDomain_0aabad08-ee57-4a66-b006-a42786ba06bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_562ff57a-bd80-4b02-8353-6a1a1975ad36" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_0aabad08-ee57-4a66-b006-a42786ba06bf" xlink:to="loc_srt_SegmentGeographicalDomain_562ff57a-bd80-4b02-8353-6a1a1975ad36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_CA_9ce3605f-a078-4ec0-8276-318a8fff28bf" xlink:href="https://xbrl.sec.gov/stpr/2021/stpr-2021.xsd#stpr_CA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_562ff57a-bd80-4b02-8353-6a1a1975ad36" xlink:to="loc_stpr_CA_9ce3605f-a078-4ec0-8276-318a8fff28bf" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/InvestmentSecuritiesAvailableforsaleSecuritiesinaContinuousUnrealizedLossPositionDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#InvestmentSecuritiesAvailableforsaleSecuritiesinaContinuousUnrealizedLossPositionDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/InvestmentSecuritiesAvailableforsaleSecuritiesinaContinuousUnrealizedLossPositionDetails" xlink:type="extended" id="iaa51a01db45847b0abe320285947b34a_InvestmentSecuritiesAvailableforsaleSecuritiesinaContinuousUnrealizedLossPositionDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_c0af18ad-c801-411b-9359-753cd89e5538" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_8f4e44f9-4b6b-4fe5-9357-7488cdca7f43" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_c0af18ad-c801-411b-9359-753cd89e5538" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_8f4e44f9-4b6b-4fe5-9357-7488cdca7f43" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_bdbd9179-7297-4122-92e3-c867feb61d92" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_c0af18ad-c801-411b-9359-753cd89e5538" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_bdbd9179-7297-4122-92e3-c867feb61d92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerFairValue_30b70c42-32a0-404c-8d49-df3a3df6717e" xlink:href="fsbc-20220930.xsd#fsbc_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_c0af18ad-c801-411b-9359-753cd89e5538" xlink:to="loc_fsbc_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerFairValue_30b70c42-32a0-404c-8d49-df3a3df6717e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_e5680f4e-f444-4248-a25b-2d06a34857c8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_c0af18ad-c801-411b-9359-753cd89e5538" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_e5680f4e-f444-4248-a25b-2d06a34857c8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_DebtSecuritiesAvailableForSaleUnrealizedLossPositionFairValue_c5e33d7d-0425-4081-b914-5265fe8b1e22" xlink:href="fsbc-20220930.xsd#fsbc_DebtSecuritiesAvailableForSaleUnrealizedLossPositionFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_c0af18ad-c801-411b-9359-753cd89e5538" xlink:to="loc_fsbc_DebtSecuritiesAvailableForSaleUnrealizedLossPositionFairValue_c5e33d7d-0425-4081-b914-5265fe8b1e22" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_380a1a95-5632-4267-87e5-786d2f0edbf4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_c0af18ad-c801-411b-9359-753cd89e5538" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_380a1a95-5632-4267-87e5-786d2f0edbf4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_21f58c53-3bfc-434a-9a05-80a6d47cf2a7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_c0af18ad-c801-411b-9359-753cd89e5538" xlink:to="loc_us-gaap_MarketableSecuritiesTable_21f58c53-3bfc-434a-9a05-80a6d47cf2a7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_63352a95-40fc-409a-a094-6b0add0dc371" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_21f58c53-3bfc-434a-9a05-80a6d47cf2a7" xlink:to="loc_us-gaap_FinancialInstrumentAxis_63352a95-40fc-409a-a094-6b0add0dc371" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_63352a95-40fc-409a-a094-6b0add0dc371_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_63352a95-40fc-409a-a094-6b0add0dc371" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_63352a95-40fc-409a-a094-6b0add0dc371_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_23e39338-a66a-4c85-9cf1-18f902f0ea53" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_63352a95-40fc-409a-a094-6b0add0dc371" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_23e39338-a66a-4c85-9cf1-18f902f0ea53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_be54c29a-d980-4ffb-85ac-44697787c68c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_23e39338-a66a-4c85-9cf1-18f902f0ea53" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_be54c29a-d980-4ffb-85ac-44697787c68c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember_f6b0aaa9-6fdf-49bd-954a-8bbf1b121979" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_23e39338-a66a-4c85-9cf1-18f902f0ea53" xlink:to="loc_us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember_f6b0aaa9-6fdf-49bd-954a-8bbf1b121979" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_56f2f670-aa2b-4c36-ad5e-0fd16e48dd59" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_23e39338-a66a-4c85-9cf1-18f902f0ea53" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_56f2f670-aa2b-4c36-ad5e-0fd16e48dd59" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralizedDebtObligationsMember_38387dbb-4ed8-4c65-815b-285dd01af103" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CollateralizedDebtObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_23e39338-a66a-4c85-9cf1-18f902f0ea53" xlink:to="loc_us-gaap_CollateralizedDebtObligationsMember_38387dbb-4ed8-4c65-815b-285dd01af103" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_6ca6ce18-21b5-4233-b9c8-81c114380135" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_23e39338-a66a-4c85-9cf1-18f902f0ea53" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_6ca6ce18-21b5-4233-b9c8-81c114380135" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/InvestmentSecuritiesNarrativeDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#InvestmentSecuritiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/InvestmentSecuritiesNarrativeDetails" xlink:type="extended" id="i7283530704754943a7b78e011b8ce602_InvestmentSecuritiesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_22b782b9-3ed6-447d-8811-296f70ea6fde" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_d89b6796-dec8-4d30-8cca-28a8b6b8db9a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_22b782b9-3ed6-447d-8811-296f70ea6fde" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_d89b6796-dec8-4d30-8cca-28a8b6b8db9a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions_6c985a7e-d952-4b88-b5e2-d38303776809" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_22b782b9-3ed6-447d-8811-296f70ea6fde" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions_6c985a7e-d952-4b88-b5e2-d38303776809" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions_d49c8b8a-08de-44d7-afe8-56c0c570814c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_22b782b9-3ed6-447d-8811-296f70ea6fde" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions_d49c8b8a-08de-44d7-afe8-56c0c570814c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_DebtSecuritiesHeldToMaturityContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions_c96e6b81-b615-4ab7-9627-8bd2c9dff46b" xlink:href="fsbc-20220930.xsd#fsbc_DebtSecuritiesHeldToMaturityContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_22b782b9-3ed6-447d-8811-296f70ea6fde" xlink:to="loc_fsbc_DebtSecuritiesHeldToMaturityContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions_c96e6b81-b615-4ab7-9627-8bd2c9dff46b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FederalHomeLoanBankAdvancesStockPriceForSalesAndPurchases_8e9a9fc9-b3e0-4c07-9991-1f1f286f192e" xlink:href="fsbc-20220930.xsd#fsbc_FederalHomeLoanBankAdvancesStockPriceForSalesAndPurchases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_22b782b9-3ed6-447d-8811-296f70ea6fde" xlink:to="loc_fsbc_FederalHomeLoanBankAdvancesStockPriceForSalesAndPurchases_8e9a9fc9-b3e0-4c07-9991-1f1f286f192e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankStock_1e4eee2d-6b2b-4e00-a75a-93dce12c2a97" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FederalHomeLoanBankStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_22b782b9-3ed6-447d-8811-296f70ea6fde" xlink:to="loc_us-gaap_FederalHomeLoanBankStock_1e4eee2d-6b2b-4e00-a75a-93dce12c2a97" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FederalHomeLoanBankStockAnnualizedDividendRatePercentage_a6028e94-a010-44e7-b1f4-5193c9deefeb" xlink:href="fsbc-20220930.xsd#fsbc_FederalHomeLoanBankStockAnnualizedDividendRatePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_22b782b9-3ed6-447d-8811-296f70ea6fde" xlink:to="loc_fsbc_FederalHomeLoanBankStockAnnualizedDividendRatePercentage_a6028e94-a010-44e7-b1f4-5193c9deefeb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FederalHomeLoanBankStockDividends_c1beb384-36c1-43f7-9678-6ed8078d7bb1" xlink:href="fsbc-20220930.xsd#fsbc_FederalHomeLoanBankStockDividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_22b782b9-3ed6-447d-8811-296f70ea6fde" xlink:to="loc_fsbc_FederalHomeLoanBankStockDividends_c1beb384-36c1-43f7-9678-6ed8078d7bb1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_d00b424f-b055-41ad-aa12-f8efa75f5f17" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_22b782b9-3ed6-447d-8811-296f70ea6fde" xlink:to="loc_us-gaap_MarketableSecuritiesTable_d00b424f-b055-41ad-aa12-f8efa75f5f17" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_31453ff0-94ff-466e-9c5f-1a8d51e3cdcc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_d00b424f-b055-41ad-aa12-f8efa75f5f17" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_31453ff0-94ff-466e-9c5f-1a8d51e3cdcc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_31453ff0-94ff-466e-9c5f-1a8d51e3cdcc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_31453ff0-94ff-466e-9c5f-1a8d51e3cdcc" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_31453ff0-94ff-466e-9c5f-1a8d51e3cdcc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_1ea2ccae-90af-4a66-b36a-7423cc5490f1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_31453ff0-94ff-466e-9c5f-1a8d51e3cdcc" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_1ea2ccae-90af-4a66-b36a-7423cc5490f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentInFederalHomeLoanBankStockMember_8e0ad0da-3abb-46b7-9817-f5533f3c71bb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InvestmentInFederalHomeLoanBankStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_1ea2ccae-90af-4a66-b36a-7423cc5490f1" xlink:to="loc_us-gaap_InvestmentInFederalHomeLoanBankStockMember_8e0ad0da-3abb-46b7-9817-f5533f3c71bb" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesNarrativeDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#LoansandAllowanceforLoanLossesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesNarrativeDetails" xlink:type="extended" id="i97664d69d3d04b7f825846658ab1a0b6_LoansandAllowanceforLoanLossesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_209dfc47-c809-447a-8bd5-470f821a6dba" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansAndLeasesReceivableNetReportedAmount_7f3e1587-9692-4101-8b8c-e9542be76323" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetReportedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_209dfc47-c809-447a-8bd5-470f821a6dba" xlink:to="loc_us-gaap_LoansAndLeasesReceivableNetReportedAmount_7f3e1587-9692-4101-8b8c-e9542be76323" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableGross_f21707db-36c9-4327-acf1-7340cd4d7281" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NotesReceivableGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_209dfc47-c809-447a-8bd5-470f821a6dba" xlink:to="loc_us-gaap_NotesReceivableGross_f21707db-36c9-4327-acf1-7340cd4d7281" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing_aac225f6-8f13-4010-9d85-e9e8571890d6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_209dfc47-c809-447a-8bd5-470f821a6dba" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing_aac225f6-8f13-4010-9d85-e9e8571890d6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableNonaccrualInterestIncome_b207c00b-a983-4a2c-b2b5-568b236938a9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableNonaccrualInterestIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_209dfc47-c809-447a-8bd5-470f821a6dba" xlink:to="loc_us-gaap_FinancingReceivableNonaccrualInterestIncome_b207c00b-a983-4a2c-b2b5-568b236938a9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1_844afb26-35d2-46fd-bc05-51d4c77e5fc1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_209dfc47-c809-447a-8bd5-470f821a6dba" xlink:to="loc_us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1_844afb26-35d2-46fd-bc05-51d4c77e5fc1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FederalReserveBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged_bf43174c-6ac2-49ef-82be-8fb0e4b81115" xlink:href="fsbc-20220930.xsd#fsbc_FederalReserveBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_209dfc47-c809-447a-8bd5-470f821a6dba" xlink:to="loc_fsbc_FederalReserveBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged_bf43174c-6ac2-49ef-82be-8fb0e4b81115" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitment_67408067-df67-484e-a87c-c71f33239492" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherCommitment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_209dfc47-c809-447a-8bd5-470f821a6dba" xlink:to="loc_us-gaap_OtherCommitment_67408067-df67-484e-a87c-c71f33239492" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_c8eea338-c616-400d-aa60-a85f9372545c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_209dfc47-c809-447a-8bd5-470f821a6dba" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_c8eea338-c616-400d-aa60-a85f9372545c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_d4e5566f-c9e3-4c60-a6f9-58951867a55f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_c8eea338-c616-400d-aa60-a85f9372545c" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_d4e5566f-c9e3-4c60-a6f9-58951867a55f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_d4e5566f-c9e3-4c60-a6f9-58951867a55f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_d4e5566f-c9e3-4c60-a6f9-58951867a55f" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_d4e5566f-c9e3-4c60-a6f9-58951867a55f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_cdfad129-4bb1-4bec-b517-d9beb4c64f72" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_d4e5566f-c9e3-4c60-a6f9-58951867a55f" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_cdfad129-4bb1-4bec-b517-d9beb4c64f72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivables60To89DaysPastDueMember_210772e2-d6a4-4a13-a68e-ade497100ce6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivables60To89DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_cdfad129-4bb1-4bec-b517-d9beb4c64f72" xlink:to="loc_us-gaap_FinancingReceivables60To89DaysPastDueMember_210772e2-d6a4-4a13-a68e-ade497100ce6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_59b2ab94-0b43-4b9b-beb7-e2ee0626127e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_c8eea338-c616-400d-aa60-a85f9372545c" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_59b2ab94-0b43-4b9b-beb7-e2ee0626127e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_59b2ab94-0b43-4b9b-beb7-e2ee0626127e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_59b2ab94-0b43-4b9b-beb7-e2ee0626127e" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_59b2ab94-0b43-4b9b-beb7-e2ee0626127e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_54d6d770-c0c7-4c6b-b051-5a3248c5e4ca" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_59b2ab94-0b43-4b9b-beb7-e2ee0626127e" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_54d6d770-c0c7-4c6b-b051-5a3248c5e4ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnfundedLoanCommitmentMember_fc64fc90-31e1-461a-a1a4-d1754e283c73" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnfundedLoanCommitmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_54d6d770-c0c7-4c6b-b051-5a3248c5e4ca" xlink:to="loc_us-gaap_UnfundedLoanCommitmentMember_fc64fc90-31e1-461a-a1a4-d1754e283c73" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_74885fe6-4e3a-4084-9fd7-110be60249ee" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_c8eea338-c616-400d-aa60-a85f9372545c" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_74885fe6-4e3a-4084-9fd7-110be60249ee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_74885fe6-4e3a-4084-9fd7-110be60249ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_74885fe6-4e3a-4084-9fd7-110be60249ee" xlink:to="loc_us-gaap_RelatedPartyDomain_74885fe6-4e3a-4084-9fd7-110be60249ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_df3b1da2-059d-441d-8186-71698e5bc0dd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_74885fe6-4e3a-4084-9fd7-110be60249ee" xlink:to="loc_us-gaap_RelatedPartyDomain_df3b1da2-059d-441d-8186-71698e5bc0dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AffiliatedEntityMember_ce0de86d-03f1-46b2-bf43-707c00931603" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_AffiliatedEntityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_df3b1da2-059d-441d-8186-71698e5bc0dd" xlink:to="loc_srt_AffiliatedEntityMember_ce0de86d-03f1-46b2-bf43-707c00931603" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FederalReserveBankBranchAxis_b42fa7eb-584f-44e3-ae9a-4de35232b256" xlink:href="fsbc-20220930.xsd#fsbc_FederalReserveBankBranchAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_c8eea338-c616-400d-aa60-a85f9372545c" xlink:to="loc_fsbc_FederalReserveBankBranchAxis_b42fa7eb-584f-44e3-ae9a-4de35232b256" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FederalReserveBankBranchDomain_b42fa7eb-584f-44e3-ae9a-4de35232b256_default" xlink:href="fsbc-20220930.xsd#fsbc_FederalReserveBankBranchDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_fsbc_FederalReserveBankBranchAxis_b42fa7eb-584f-44e3-ae9a-4de35232b256" xlink:to="loc_fsbc_FederalReserveBankBranchDomain_b42fa7eb-584f-44e3-ae9a-4de35232b256_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FederalReserveBankBranchDomain_48ee9709-f718-4717-99b5-764223b25d7c" xlink:href="fsbc-20220930.xsd#fsbc_FederalReserveBankBranchDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_fsbc_FederalReserveBankBranchAxis_b42fa7eb-584f-44e3-ae9a-4de35232b256" xlink:to="loc_fsbc_FederalReserveBankBranchDomain_48ee9709-f718-4717-99b5-764223b25d7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FederalReserveBankOfSanFranciscoMember_b44b9cb5-f21a-4180-94e1-93da7fff1c50" xlink:href="fsbc-20220930.xsd#fsbc_FederalReserveBankOfSanFranciscoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsbc_FederalReserveBankBranchDomain_48ee9709-f718-4717-99b5-764223b25d7c" xlink:to="loc_fsbc_FederalReserveBankOfSanFranciscoMember_b44b9cb5-f21a-4180-94e1-93da7fff1c50" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesBalanceofEachMajorProductTypeDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#LoansandAllowanceforLoanLossesBalanceofEachMajorProductTypeDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesBalanceofEachMajorProductTypeDetails" xlink:type="extended" id="i1b622355ea394e60bd57e84aa1b76bc7_LoansandAllowanceforLoanLossesBalanceofEachMajorProductTypeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_97750694-6bfe-48e5-8deb-0323fdc1dad9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansAndLeasesReceivableGrossCarryingAmount_9fc1403f-e853-4b09-8a71-0030393ee46a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansAndLeasesReceivableGrossCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_97750694-6bfe-48e5-8deb-0323fdc1dad9" xlink:to="loc_us-gaap_LoansAndLeasesReceivableGrossCarryingAmount_9fc1403f-e853-4b09-8a71-0030393ee46a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansAndLeasesReceivableDeferredIncome_029f6a90-78be-446d-8777-b83bc464e188" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansAndLeasesReceivableDeferredIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_97750694-6bfe-48e5-8deb-0323fdc1dad9" xlink:to="loc_us-gaap_LoansAndLeasesReceivableDeferredIncome_029f6a90-78be-446d-8777-b83bc464e188" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansAndLeasesReceivableAllowance_83381fd4-9b10-4935-85d9-6b58f4b4a36c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansAndLeasesReceivableAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_97750694-6bfe-48e5-8deb-0323fdc1dad9" xlink:to="loc_us-gaap_LoansAndLeasesReceivableAllowance_83381fd4-9b10-4935-85d9-6b58f4b4a36c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansAndLeasesReceivableNetReportedAmount_51e5b9d8-e3c7-4256-8968-499cddcf4dc7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetReportedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_97750694-6bfe-48e5-8deb-0323fdc1dad9" xlink:to="loc_us-gaap_LoansAndLeasesReceivableNetReportedAmount_51e5b9d8-e3c7-4256-8968-499cddcf4dc7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_ab1e4608-2051-40be-a8d2-8bc8f6988f02" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_97750694-6bfe-48e5-8deb-0323fdc1dad9" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_ab1e4608-2051-40be-a8d2-8bc8f6988f02" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_af0a10da-de40-4fd0-98be-cbac7506616e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_ab1e4608-2051-40be-a8d2-8bc8f6988f02" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_af0a10da-de40-4fd0-98be-cbac7506616e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_af0a10da-de40-4fd0-98be-cbac7506616e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_af0a10da-de40-4fd0-98be-cbac7506616e" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_af0a10da-de40-4fd0-98be-cbac7506616e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_1646dc43-74d4-454e-ac0b-5a7da0686764" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_af0a10da-de40-4fd0-98be-cbac7506616e" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_1646dc43-74d4-454e-ac0b-5a7da0686764" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstateMember_0b69d287-e327-42b5-a3fd-fbcd8fb4f6ef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommercialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_1646dc43-74d4-454e-ac0b-5a7da0686764" xlink:to="loc_us-gaap_CommercialRealEstateMember_0b69d287-e327-42b5-a3fd-fbcd8fb4f6ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_RealEstateCommercialLandAndDevelopmentMember_eac413df-73be-45f6-8c54-103b8ce7a839" xlink:href="fsbc-20220930.xsd#fsbc_RealEstateCommercialLandAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_1646dc43-74d4-454e-ac0b-5a7da0686764" xlink:to="loc_fsbc_RealEstateCommercialLandAndDevelopmentMember_eac413df-73be-45f6-8c54-103b8ce7a839" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_CommercialConstructionLoansMember_a7709566-696c-4857-8ac8-0713f6247467" xlink:href="fsbc-20220930.xsd#fsbc_CommercialConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_1646dc43-74d4-454e-ac0b-5a7da0686764" xlink:to="loc_fsbc_CommercialConstructionLoansMember_a7709566-696c-4857-8ac8-0713f6247467" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_ResidentialConstructionLoansMember_cbdf8e12-0901-4d52-b10a-4f5fe3f1e18c" xlink:href="fsbc-20220930.xsd#fsbc_ResidentialConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_1646dc43-74d4-454e-ac0b-5a7da0686764" xlink:to="loc_fsbc_ResidentialConstructionLoansMember_cbdf8e12-0901-4d52-b10a-4f5fe3f1e18c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialRealEstateMember_2c8db363-c0d2-4329-ba2e-b924187957a3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResidentialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_1646dc43-74d4-454e-ac0b-5a7da0686764" xlink:to="loc_us-gaap_ResidentialRealEstateMember_2c8db363-c0d2-4329-ba2e-b924187957a3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FarmlandMember_8a0d3ef3-2e30-4bc9-b316-5daf0c703219" xlink:href="fsbc-20220930.xsd#fsbc_FarmlandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_1646dc43-74d4-454e-ac0b-5a7da0686764" xlink:to="loc_fsbc_FarmlandMember_8a0d3ef3-2e30-4bc9-b316-5daf0c703219" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_e593c42b-e86f-4dd0-80cd-d3ad81c31461" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_1646dc43-74d4-454e-ac0b-5a7da0686764" xlink:to="loc_us-gaap_SecuredDebtMember_e593c42b-e86f-4dd0-80cd-d3ad81c31461" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_b59dbb23-2706-4dfe-ba4b-1d8d4731008d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_1646dc43-74d4-454e-ac0b-5a7da0686764" xlink:to="loc_us-gaap_UnsecuredDebtMember_b59dbb23-2706-4dfe-ba4b-1d8d4731008d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_CommercialPaycheckProtectionProgramMember_a43a8bad-ecdc-4505-aba4-5bd4a1f70ffa" xlink:href="fsbc-20220930.xsd#fsbc_CommercialPaycheckProtectionProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_1646dc43-74d4-454e-ac0b-5a7da0686764" xlink:to="loc_fsbc_CommercialPaycheckProtectionProgramMember_a43a8bad-ecdc-4505-aba4-5bd4a1f70ffa" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_c1f1a189-9335-49b8-bf3d-48e8744b8fa3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_1646dc43-74d4-454e-ac0b-5a7da0686764" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_c1f1a189-9335-49b8-bf3d-48e8744b8fa3" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesCreditQualityIndicatorsRelatedtotheCompanysLoansbyClassDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#LoansandAllowanceforLoanLossesCreditQualityIndicatorsRelatedtotheCompanysLoansbyClassDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesCreditQualityIndicatorsRelatedtotheCompanysLoansbyClassDetails" xlink:type="extended" id="idf0a9d0a9ba34181bfd284c5f10a23ab_LoansandAllowanceforLoanLossesCreditQualityIndicatorsRelatedtotheCompanysLoansbyClassDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_59e9cc71-4746-4694-b520-d4dfe87fe2cd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansAndLeasesReceivableGrossCarryingAmount_29c0cecd-8b76-4507-aefe-422b78092c27" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansAndLeasesReceivableGrossCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_59e9cc71-4746-4694-b520-d4dfe87fe2cd" xlink:to="loc_us-gaap_LoansAndLeasesReceivableGrossCarryingAmount_29c0cecd-8b76-4507-aefe-422b78092c27" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_1ccecd21-3c00-4845-908c-9e1f8ebe7866" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_59e9cc71-4746-4694-b520-d4dfe87fe2cd" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_1ccecd21-3c00-4845-908c-9e1f8ebe7866" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_5b4364d6-3307-49fa-a667-d1fead30f909" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_1ccecd21-3c00-4845-908c-9e1f8ebe7866" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_5b4364d6-3307-49fa-a667-d1fead30f909" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_5b4364d6-3307-49fa-a667-d1fead30f909_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_5b4364d6-3307-49fa-a667-d1fead30f909" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_5b4364d6-3307-49fa-a667-d1fead30f909_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_f8566866-5318-495a-975a-71fddf3a2cce" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_5b4364d6-3307-49fa-a667-d1fead30f909" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_f8566866-5318-495a-975a-71fddf3a2cce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstateMember_30fe7c26-48ed-49da-97c2-13bb43699263" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommercialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_f8566866-5318-495a-975a-71fddf3a2cce" xlink:to="loc_us-gaap_CommercialRealEstateMember_30fe7c26-48ed-49da-97c2-13bb43699263" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_RealEstateCommercialLandAndDevelopmentMember_fe1ea169-0a4a-4c16-b7ae-8ba90a9c06a4" xlink:href="fsbc-20220930.xsd#fsbc_RealEstateCommercialLandAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_f8566866-5318-495a-975a-71fddf3a2cce" xlink:to="loc_fsbc_RealEstateCommercialLandAndDevelopmentMember_fe1ea169-0a4a-4c16-b7ae-8ba90a9c06a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_CommercialConstructionLoansMember_e8cd905e-f413-4ad5-97a8-8ab63d02a79c" xlink:href="fsbc-20220930.xsd#fsbc_CommercialConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_f8566866-5318-495a-975a-71fddf3a2cce" xlink:to="loc_fsbc_CommercialConstructionLoansMember_e8cd905e-f413-4ad5-97a8-8ab63d02a79c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_ResidentialConstructionLoansMember_82f03a80-5fec-4f88-bd28-201c648118ed" xlink:href="fsbc-20220930.xsd#fsbc_ResidentialConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_f8566866-5318-495a-975a-71fddf3a2cce" xlink:to="loc_fsbc_ResidentialConstructionLoansMember_82f03a80-5fec-4f88-bd28-201c648118ed" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialRealEstateMember_257d8adc-ab42-408a-af3f-b13a477580de" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResidentialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_f8566866-5318-495a-975a-71fddf3a2cce" xlink:to="loc_us-gaap_ResidentialRealEstateMember_257d8adc-ab42-408a-af3f-b13a477580de" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FarmlandMember_3f8c7f03-2e27-46fe-b695-fecebb62891a" xlink:href="fsbc-20220930.xsd#fsbc_FarmlandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_f8566866-5318-495a-975a-71fddf3a2cce" xlink:to="loc_fsbc_FarmlandMember_3f8c7f03-2e27-46fe-b695-fecebb62891a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_3a095e3d-b2fd-46a5-9acf-db57eecc02ba" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_f8566866-5318-495a-975a-71fddf3a2cce" xlink:to="loc_us-gaap_SecuredDebtMember_3a095e3d-b2fd-46a5-9acf-db57eecc02ba" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_ecf85c29-bb93-4d97-bced-36e8270f155c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_f8566866-5318-495a-975a-71fddf3a2cce" xlink:to="loc_us-gaap_UnsecuredDebtMember_ecf85c29-bb93-4d97-bced-36e8270f155c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_CommercialPaycheckProtectionProgramMember_c4c4ddd9-392c-4350-9df3-b5b795bd4414" xlink:href="fsbc-20220930.xsd#fsbc_CommercialPaycheckProtectionProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_f8566866-5318-495a-975a-71fddf3a2cce" xlink:to="loc_fsbc_CommercialPaycheckProtectionProgramMember_c4c4ddd9-392c-4350-9df3-b5b795bd4414" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_662949a1-3c36-41b9-98f3-30eec39f7e71" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_f8566866-5318-495a-975a-71fddf3a2cce" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_662949a1-3c36-41b9-98f3-30eec39f7e71" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentAxis_acb48175-ceca-4bec-9446-7617fcf1a0f6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InternalCreditAssessmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_1ccecd21-3c00-4845-908c-9e1f8ebe7866" xlink:to="loc_us-gaap_InternalCreditAssessmentAxis_acb48175-ceca-4bec-9446-7617fcf1a0f6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentDomain_acb48175-ceca-4bec-9446-7617fcf1a0f6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InternalCreditAssessmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InternalCreditAssessmentAxis_acb48175-ceca-4bec-9446-7617fcf1a0f6" xlink:to="loc_us-gaap_InternalCreditAssessmentDomain_acb48175-ceca-4bec-9446-7617fcf1a0f6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentDomain_1994b20c-d519-47f7-99ff-15ca922a082a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InternalCreditAssessmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InternalCreditAssessmentAxis_acb48175-ceca-4bec-9446-7617fcf1a0f6" xlink:to="loc_us-gaap_InternalCreditAssessmentDomain_1994b20c-d519-47f7-99ff-15ca922a082a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PassMember_a156f72a-b2ea-4a5d-ba7a-d146dc91826d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PassMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_1994b20c-d519-47f7-99ff-15ca922a082a" xlink:to="loc_us-gaap_PassMember_a156f72a-b2ea-4a5d-ba7a-d146dc91826d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_WatchMember_193d82c0-f8a2-4a8a-85bf-40e1015ebabd" xlink:href="fsbc-20220930.xsd#fsbc_WatchMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_1994b20c-d519-47f7-99ff-15ca922a082a" xlink:to="loc_fsbc_WatchMember_193d82c0-f8a2-4a8a-85bf-40e1015ebabd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubstandardMember_3ebe1fc2-b76c-419a-9a21-f69164d387db" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubstandardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_1994b20c-d519-47f7-99ff-15ca922a082a" xlink:to="loc_us-gaap_SubstandardMember_3ebe1fc2-b76c-419a-9a21-f69164d387db" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DoubtfulMember_1b51b7fa-3705-4c07-92e5-799f4e7573bc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DoubtfulMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_1994b20c-d519-47f7-99ff-15ca922a082a" xlink:to="loc_us-gaap_DoubtfulMember_1b51b7fa-3705-4c07-92e5-799f4e7573bc" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesAgeAnalysisofPastDueLoansbyClassDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#LoansandAllowanceforLoanLossesAgeAnalysisofPastDueLoansbyClassDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesAgeAnalysisofPastDueLoansbyClassDetails" xlink:type="extended" id="i85f6fc3691484d4fa0fb443b72718f8a_LoansandAllowanceforLoanLossesAgeAnalysisofPastDueLoansbyClassDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_016c74ee-3f7b-4251-8eb3-25f13ae0099e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansAndLeasesReceivableGrossCarryingAmount_7ce9b3e2-56ff-480d-9b26-429ee30539c7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansAndLeasesReceivableGrossCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_016c74ee-3f7b-4251-8eb3-25f13ae0099e" xlink:to="loc_us-gaap_LoansAndLeasesReceivableGrossCarryingAmount_7ce9b3e2-56ff-480d-9b26-429ee30539c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_04a8c48d-19c3-42be-982e-742152965062" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_016c74ee-3f7b-4251-8eb3-25f13ae0099e" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_04a8c48d-19c3-42be-982e-742152965062" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_beb3c620-93fd-488f-aa34-4c8c0da6761f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_04a8c48d-19c3-42be-982e-742152965062" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_beb3c620-93fd-488f-aa34-4c8c0da6761f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_beb3c620-93fd-488f-aa34-4c8c0da6761f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_beb3c620-93fd-488f-aa34-4c8c0da6761f" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_beb3c620-93fd-488f-aa34-4c8c0da6761f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_31be0a79-1916-41e2-b2da-0a3b78fd12bf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_beb3c620-93fd-488f-aa34-4c8c0da6761f" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_31be0a79-1916-41e2-b2da-0a3b78fd12bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstateMember_8085c2e8-e78b-4846-a71e-a9fed7702705" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommercialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_31be0a79-1916-41e2-b2da-0a3b78fd12bf" xlink:to="loc_us-gaap_CommercialRealEstateMember_8085c2e8-e78b-4846-a71e-a9fed7702705" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_RealEstateCommercialLandAndDevelopmentMember_0009219d-ac83-4045-bcb1-d11ebc3db065" xlink:href="fsbc-20220930.xsd#fsbc_RealEstateCommercialLandAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_31be0a79-1916-41e2-b2da-0a3b78fd12bf" xlink:to="loc_fsbc_RealEstateCommercialLandAndDevelopmentMember_0009219d-ac83-4045-bcb1-d11ebc3db065" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_CommercialConstructionLoansMember_655920e4-e6a3-4ba9-b20d-73deac71cbe7" xlink:href="fsbc-20220930.xsd#fsbc_CommercialConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_31be0a79-1916-41e2-b2da-0a3b78fd12bf" xlink:to="loc_fsbc_CommercialConstructionLoansMember_655920e4-e6a3-4ba9-b20d-73deac71cbe7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_ResidentialConstructionLoansMember_eff4331a-eeff-494b-bba6-f0e6876a48be" xlink:href="fsbc-20220930.xsd#fsbc_ResidentialConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_31be0a79-1916-41e2-b2da-0a3b78fd12bf" xlink:to="loc_fsbc_ResidentialConstructionLoansMember_eff4331a-eeff-494b-bba6-f0e6876a48be" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialRealEstateMember_ccd3da02-2400-4751-bac7-28e841adca15" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResidentialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_31be0a79-1916-41e2-b2da-0a3b78fd12bf" xlink:to="loc_us-gaap_ResidentialRealEstateMember_ccd3da02-2400-4751-bac7-28e841adca15" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FarmlandMember_fc433541-0872-457f-9a30-7763cb3d71d7" xlink:href="fsbc-20220930.xsd#fsbc_FarmlandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_31be0a79-1916-41e2-b2da-0a3b78fd12bf" xlink:to="loc_fsbc_FarmlandMember_fc433541-0872-457f-9a30-7763cb3d71d7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_ef2a9021-4bfd-48ba-a027-0114f6810c78" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_31be0a79-1916-41e2-b2da-0a3b78fd12bf" xlink:to="loc_us-gaap_SecuredDebtMember_ef2a9021-4bfd-48ba-a027-0114f6810c78" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_84360d60-d90d-4c3d-8e0d-ac725de301d0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_31be0a79-1916-41e2-b2da-0a3b78fd12bf" xlink:to="loc_us-gaap_UnsecuredDebtMember_84360d60-d90d-4c3d-8e0d-ac725de301d0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_CommercialPaycheckProtectionProgramMember_bcd97aa2-893b-4a32-b37c-aad170a440e4" xlink:href="fsbc-20220930.xsd#fsbc_CommercialPaycheckProtectionProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_31be0a79-1916-41e2-b2da-0a3b78fd12bf" xlink:to="loc_fsbc_CommercialPaycheckProtectionProgramMember_bcd97aa2-893b-4a32-b37c-aad170a440e4" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_6fe04c40-6bf0-46c2-8379-435cb48523fe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_31be0a79-1916-41e2-b2da-0a3b78fd12bf" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_6fe04c40-6bf0-46c2-8379-435cb48523fe" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_0994b4fe-4016-481f-8238-8eb2718c5d80" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_04a8c48d-19c3-42be-982e-742152965062" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_0994b4fe-4016-481f-8238-8eb2718c5d80" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_0994b4fe-4016-481f-8238-8eb2718c5d80_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_0994b4fe-4016-481f-8238-8eb2718c5d80" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_0994b4fe-4016-481f-8238-8eb2718c5d80_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_bfe5b149-4a6e-4b4f-8583-31962055b15f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_0994b4fe-4016-481f-8238-8eb2718c5d80" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_bfe5b149-4a6e-4b4f-8583-31962055b15f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FinancingReceivables30To89DaysPastDueMember_77ca885d-42c7-40b6-ad58-4b698c110ce2" xlink:href="fsbc-20220930.xsd#fsbc_FinancingReceivables30To89DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_bfe5b149-4a6e-4b4f-8583-31962055b15f" xlink:to="loc_fsbc_FinancingReceivables30To89DaysPastDueMember_77ca885d-42c7-40b6-ad58-4b698c110ce2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_be0821b4-02f4-46d2-b62a-8b8e0f354c12" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_bfe5b149-4a6e-4b4f-8583-31962055b15f" xlink:to="loc_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_be0821b4-02f4-46d2-b62a-8b8e0f354c12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialAssetPastDueMember_5470f29b-644b-4e42-91bb-a0f926cecb1e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialAssetPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_bfe5b149-4a6e-4b4f-8583-31962055b15f" xlink:to="loc_us-gaap_FinancialAssetPastDueMember_5470f29b-644b-4e42-91bb-a0f926cecb1e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialAssetNotPastDueMember_3d7a1b23-4dfc-4f00-97ef-5c4478c41289" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialAssetNotPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_bfe5b149-4a6e-4b4f-8583-31962055b15f" xlink:to="loc_us-gaap_FinancialAssetNotPastDueMember_3d7a1b23-4dfc-4f00-97ef-5c4478c41289" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesImpairedLoansDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#LoansandAllowanceforLoanLossesImpairedLoansDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesImpairedLoansDetails" xlink:type="extended" id="i9289499fdfe849e1b18167ccc9dd305f_LoansandAllowanceforLoanLossesImpairedLoansDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_9038439e-ec75-4b00-b511-ca5b14721826" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableRecordedInvestmentAbstract_7a0f61f4-9a25-46b9-8c88-b9146b98ea6d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableRecordedInvestmentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_9038439e-ec75-4b00-b511-ca5b14721826" xlink:to="loc_us-gaap_ImpairedFinancingReceivableRecordedInvestmentAbstract_7a0f61f4-9a25-46b9-8c88-b9146b98ea6d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment_b8f3d33b-e31c-4031-ad0a-22865a001433" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairedFinancingReceivableRecordedInvestmentAbstract_7a0f61f4-9a25-46b9-8c88-b9146b98ea6d" xlink:to="loc_us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment_b8f3d33b-e31c-4031-ad0a-22865a001433" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment_ab9ab518-403b-4efe-8634-1e840f4ebd47" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairedFinancingReceivableRecordedInvestmentAbstract_7a0f61f4-9a25-46b9-8c88-b9146b98ea6d" xlink:to="loc_us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment_ab9ab518-403b-4efe-8634-1e840f4ebd47" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableRecordedInvestment_33955d33-7f67-465d-af3e-ad4f16dbb2af" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableRecordedInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairedFinancingReceivableRecordedInvestmentAbstract_7a0f61f4-9a25-46b9-8c88-b9146b98ea6d" xlink:to="loc_us-gaap_ImpairedFinancingReceivableRecordedInvestment_33955d33-7f67-465d-af3e-ad4f16dbb2af" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalanceAbstract_4cfa5f74-f379-4f2f-b821-e689182eccb7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalanceAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_9038439e-ec75-4b00-b511-ca5b14721826" xlink:to="loc_us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalanceAbstract_4cfa5f74-f379-4f2f-b821-e689182eccb7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance_0236f553-3c52-42fd-88d9-45446d27693d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalanceAbstract_4cfa5f74-f379-4f2f-b821-e689182eccb7" xlink:to="loc_us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance_0236f553-3c52-42fd-88d9-45446d27693d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance_e6db303a-6ebc-4c7d-8291-b0500a017949" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalanceAbstract_4cfa5f74-f379-4f2f-b821-e689182eccb7" xlink:to="loc_us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance_e6db303a-6ebc-4c7d-8291-b0500a017949" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance_0d1865f4-2ea4-480b-8b59-2f78cfdafdc8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalanceAbstract_4cfa5f74-f379-4f2f-b821-e689182eccb7" xlink:to="loc_us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance_0d1865f4-2ea4-480b-8b59-2f78cfdafdc8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableRelatedAllowance_2ffd4170-8373-41dc-9f0b-700c5c5aed87" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableRelatedAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_9038439e-ec75-4b00-b511-ca5b14721826" xlink:to="loc_us-gaap_ImpairedFinancingReceivableRelatedAllowance_2ffd4170-8373-41dc-9f0b-700c5c5aed87" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableAverageRecordedInvestmentAbstract_9d30a41e-d0c5-4835-b483-10e2975dbe01" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableAverageRecordedInvestmentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_9038439e-ec75-4b00-b511-ca5b14721826" xlink:to="loc_us-gaap_ImpairedFinancingReceivableAverageRecordedInvestmentAbstract_9d30a41e-d0c5-4835-b483-10e2975dbe01" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment_861956c4-01a6-4876-9b12-96a567f7495b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairedFinancingReceivableAverageRecordedInvestmentAbstract_9d30a41e-d0c5-4835-b483-10e2975dbe01" xlink:to="loc_us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment_861956c4-01a6-4876-9b12-96a567f7495b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment_ac86500d-5589-495c-8ff4-369f3ddb8be4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairedFinancingReceivableAverageRecordedInvestmentAbstract_9d30a41e-d0c5-4835-b483-10e2975dbe01" xlink:to="loc_us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment_ac86500d-5589-495c-8ff4-369f3ddb8be4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment_83f4c2d2-0c87-48dc-9771-390528cc27a1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairedFinancingReceivableAverageRecordedInvestmentAbstract_9d30a41e-d0c5-4835-b483-10e2975dbe01" xlink:to="loc_us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment_83f4c2d2-0c87-48dc-9771-390528cc27a1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethodAbstract_73782720-e116-473c-b7e1-4b7537ad1d82" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethodAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_9038439e-ec75-4b00-b511-ca5b14721826" xlink:to="loc_us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethodAbstract_73782720-e116-473c-b7e1-4b7537ad1d82" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeAccrualMethod_005a9dd9-e14f-4946-9976-67c2cf42304b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeAccrualMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethodAbstract_73782720-e116-473c-b7e1-4b7537ad1d82" xlink:to="loc_us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeAccrualMethod_005a9dd9-e14f-4946-9976-67c2cf42304b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeAccrualMethod_2638410e-8906-43be-8e4b-fa80ac4665a9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeAccrualMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethodAbstract_73782720-e116-473c-b7e1-4b7537ad1d82" xlink:to="loc_us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeAccrualMethod_2638410e-8906-43be-8e4b-fa80ac4665a9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod_5d396d22-8ebe-42e9-a4ab-f3247be31eb6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethodAbstract_73782720-e116-473c-b7e1-4b7537ad1d82" xlink:to="loc_us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod_5d396d22-8ebe-42e9-a4ab-f3247be31eb6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_6b6404b8-4462-4d01-b9c2-04b7ac80622f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_9038439e-ec75-4b00-b511-ca5b14721826" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_6b6404b8-4462-4d01-b9c2-04b7ac80622f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_3c247269-a48d-4812-8379-6915a4b075a9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_6b6404b8-4462-4d01-b9c2-04b7ac80622f" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_3c247269-a48d-4812-8379-6915a4b075a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_3c247269-a48d-4812-8379-6915a4b075a9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_3c247269-a48d-4812-8379-6915a4b075a9" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_3c247269-a48d-4812-8379-6915a4b075a9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_5b4ff7d3-6dc5-45d3-aa65-0929bdd6c34c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_3c247269-a48d-4812-8379-6915a4b075a9" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_5b4ff7d3-6dc5-45d3-aa65-0929bdd6c34c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstateMember_39e14112-cf26-4516-94f0-d2336e6102c2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommercialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_5b4ff7d3-6dc5-45d3-aa65-0929bdd6c34c" xlink:to="loc_us-gaap_CommercialRealEstateMember_39e14112-cf26-4516-94f0-d2336e6102c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialRealEstateMember_c3ff3da1-813d-4aa7-a86c-2698ac29bbc7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResidentialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_5b4ff7d3-6dc5-45d3-aa65-0929bdd6c34c" xlink:to="loc_us-gaap_ResidentialRealEstateMember_c3ff3da1-813d-4aa7-a86c-2698ac29bbc7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_517607f8-d96d-49ca-909d-41046e965008" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_5b4ff7d3-6dc5-45d3-aa65-0929bdd6c34c" xlink:to="loc_us-gaap_SecuredDebtMember_517607f8-d96d-49ca-909d-41046e965008" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_ConsumerAndOtherMember_eeda00f4-b129-4360-a2bf-dc6f75ba65e9" xlink:href="fsbc-20220930.xsd#fsbc_ConsumerAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_5b4ff7d3-6dc5-45d3-aa65-0929bdd6c34c" xlink:to="loc_fsbc_ConsumerAndOtherMember_eeda00f4-b129-4360-a2bf-dc6f75ba65e9" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesNonaccrualLoansSegregatedbyClassDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#LoansandAllowanceforLoanLossesNonaccrualLoansSegregatedbyClassDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesNonaccrualLoansSegregatedbyClassDetails" xlink:type="extended" id="i708feb6c2acd41de98011da882bc31c0_LoansandAllowanceforLoanLossesNonaccrualLoansSegregatedbyClassDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_96bdfde3-d1c2-49e9-9095-9e7490b804a7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus_75b243ac-10cb-46c0-8f87-1429cb154441" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_96bdfde3-d1c2-49e9-9095-9e7490b804a7" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus_75b243ac-10cb-46c0-8f87-1429cb154441" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_2930b98b-a42d-4a24-8d12-26e258b012ab" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_96bdfde3-d1c2-49e9-9095-9e7490b804a7" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_2930b98b-a42d-4a24-8d12-26e258b012ab" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_5d3cfb8b-a93c-497b-b4b4-d9522ba6eaf1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_2930b98b-a42d-4a24-8d12-26e258b012ab" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_5d3cfb8b-a93c-497b-b4b4-d9522ba6eaf1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_5d3cfb8b-a93c-497b-b4b4-d9522ba6eaf1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_5d3cfb8b-a93c-497b-b4b4-d9522ba6eaf1" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_5d3cfb8b-a93c-497b-b4b4-d9522ba6eaf1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_773a44ff-14ca-40a0-b8a8-c67589ae5532" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_5d3cfb8b-a93c-497b-b4b4-d9522ba6eaf1" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_773a44ff-14ca-40a0-b8a8-c67589ae5532" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstateMember_7bec789f-fe43-446c-abb9-c2a4abdd7219" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommercialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_773a44ff-14ca-40a0-b8a8-c67589ae5532" xlink:to="loc_us-gaap_CommercialRealEstateMember_7bec789f-fe43-446c-abb9-c2a4abdd7219" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialRealEstateMember_92bc1411-cf53-4e12-94c0-9c1cd782a0f4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResidentialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_773a44ff-14ca-40a0-b8a8-c67589ae5532" xlink:to="loc_us-gaap_ResidentialRealEstateMember_92bc1411-cf53-4e12-94c0-9c1cd782a0f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_08f0e9d8-b215-4500-9a55-e305b515340d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_773a44ff-14ca-40a0-b8a8-c67589ae5532" xlink:to="loc_us-gaap_SecuredDebtMember_08f0e9d8-b215-4500-9a55-e305b515340d" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesAllowanceforLoanLossesDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#LoansandAllowanceforLoanLossesAllowanceforLoanLossesDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesAllowanceforLoanLossesDetails" xlink:type="extended" id="i2639c4629a7b4643afadce717c2238c5_LoansandAllowanceforLoanLossesAllowanceforLoanLossesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_dfa46eb3-9699-4fe1-ab68-1f0ce652d306" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_a66c250d-920d-40b1-b748-c473e6892d69" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_dfa46eb3-9699-4fe1-ab68-1f0ce652d306" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_a66c250d-920d-40b1-b748-c473e6892d69" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansAndLeasesReceivableAllowance_2e468c6a-4913-4df7-8660-c5792e79f0d6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansAndLeasesReceivableAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_a66c250d-920d-40b1-b748-c473e6892d69" xlink:to="loc_us-gaap_LoansAndLeasesReceivableAllowance_2e468c6a-4913-4df7-8660-c5792e79f0d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs_edf89a10-496a-4a3f-8ff0-6a55e75bf7f8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_a66c250d-920d-40b1-b748-c473e6892d69" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs_edf89a10-496a-4a3f-8ff0-6a55e75bf7f8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery_f1734ed4-956a-460b-a485-56e0f9f402bc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_a66c250d-920d-40b1-b748-c473e6892d69" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery_f1734ed4-956a-460b-a485-56e0f9f402bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForLoanAndLeaseLosses_3d63ac77-b74b-4349-9363-be8415020324" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProvisionForLoanAndLeaseLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_a66c250d-920d-40b1-b748-c473e6892d69" xlink:to="loc_us-gaap_ProvisionForLoanAndLeaseLosses_3d63ac77-b74b-4349-9363-be8415020324" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansAndLeasesReceivableAllowance_1469dff7-392a-40e4-bfa2-c6c019ea430b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansAndLeasesReceivableAllowance"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_b5272ccc-7987-4eb4-a7bf-d8835988b35b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_dfa46eb3-9699-4fe1-ab68-1f0ce652d306" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_b5272ccc-7987-4eb4-a7bf-d8835988b35b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_06c1554c-6de4-45f7-a9ca-03467f6d3a84" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_b5272ccc-7987-4eb4-a7bf-d8835988b35b" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_06c1554c-6de4-45f7-a9ca-03467f6d3a84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_06c1554c-6de4-45f7-a9ca-03467f6d3a84_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_06c1554c-6de4-45f7-a9ca-03467f6d3a84" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_06c1554c-6de4-45f7-a9ca-03467f6d3a84_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_b3d319d5-04ee-4f83-8787-13561d31f8d1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_06c1554c-6de4-45f7-a9ca-03467f6d3a84" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_b3d319d5-04ee-4f83-8787-13561d31f8d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstateMember_f5c52afb-188e-4e9a-a5e4-42d246985258" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommercialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_b3d319d5-04ee-4f83-8787-13561d31f8d1" xlink:to="loc_us-gaap_CommercialRealEstateMember_f5c52afb-188e-4e9a-a5e4-42d246985258" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_RealEstateCommercialLandAndDevelopmentMember_015cb90c-f5dd-4899-bcbf-36ff24167428" xlink:href="fsbc-20220930.xsd#fsbc_RealEstateCommercialLandAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_b3d319d5-04ee-4f83-8787-13561d31f8d1" xlink:to="loc_fsbc_RealEstateCommercialLandAndDevelopmentMember_015cb90c-f5dd-4899-bcbf-36ff24167428" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_CommercialConstructionLoansMember_49bbdc32-dea1-409b-ac6d-496ab8cb797d" xlink:href="fsbc-20220930.xsd#fsbc_CommercialConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_b3d319d5-04ee-4f83-8787-13561d31f8d1" xlink:to="loc_fsbc_CommercialConstructionLoansMember_49bbdc32-dea1-409b-ac6d-496ab8cb797d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_ResidentialConstructionLoansMember_8083489a-6bac-4a0b-86c5-38f17d9617e3" xlink:href="fsbc-20220930.xsd#fsbc_ResidentialConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_b3d319d5-04ee-4f83-8787-13561d31f8d1" xlink:to="loc_fsbc_ResidentialConstructionLoansMember_8083489a-6bac-4a0b-86c5-38f17d9617e3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialRealEstateMember_2111c063-8fed-44c1-9439-9d5d5c0c049a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResidentialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_b3d319d5-04ee-4f83-8787-13561d31f8d1" xlink:to="loc_us-gaap_ResidentialRealEstateMember_2111c063-8fed-44c1-9439-9d5d5c0c049a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FarmlandMember_add2ec7b-6615-4210-8a7e-d36a708021b1" xlink:href="fsbc-20220930.xsd#fsbc_FarmlandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_b3d319d5-04ee-4f83-8787-13561d31f8d1" xlink:to="loc_fsbc_FarmlandMember_add2ec7b-6615-4210-8a7e-d36a708021b1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_a3707243-0997-411b-8ca4-9409f6ae97dd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_b3d319d5-04ee-4f83-8787-13561d31f8d1" xlink:to="loc_us-gaap_SecuredDebtMember_a3707243-0997-411b-8ca4-9409f6ae97dd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_08f4cbfb-1d3a-4b71-b53a-8e88998c97fc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_b3d319d5-04ee-4f83-8787-13561d31f8d1" xlink:to="loc_us-gaap_UnsecuredDebtMember_08f4cbfb-1d3a-4b71-b53a-8e88998c97fc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_CommercialPaycheckProtectionProgramMember_6d6bff21-c576-480f-ae1c-f8408207e7b8" xlink:href="fsbc-20220930.xsd#fsbc_CommercialPaycheckProtectionProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_b3d319d5-04ee-4f83-8787-13561d31f8d1" xlink:to="loc_fsbc_CommercialPaycheckProtectionProgramMember_6d6bff21-c576-480f-ae1c-f8408207e7b8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_c13f3af0-2303-4192-99cc-f0ba56458348" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_b3d319d5-04ee-4f83-8787-13561d31f8d1" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_c13f3af0-2303-4192-99cc-f0ba56458348" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnallocatedFinancingReceivablesMember_35e8d254-5cbb-4f65-bd45-68048181fc1e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnallocatedFinancingReceivablesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_b3d319d5-04ee-4f83-8787-13561d31f8d1" xlink:to="loc_us-gaap_UnallocatedFinancingReceivablesMember_35e8d254-5cbb-4f65-bd45-68048181fc1e" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesAllocationofLoanLossesDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#LoansandAllowanceforLoanLossesAllocationofLoanLossesDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/LoansandAllowanceforLoanLossesAllocationofLoanLossesDetails" xlink:type="extended" id="i3c5daba2fff44b738c9feeae78f66386_LoansandAllowanceforLoanLossesAllocationofLoanLossesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_bac5675b-673f-4422-86aa-a73cbac27bfa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1_abdb5da0-2e0b-4770-b135-e1b75b763efc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_bac5675b-673f-4422-86aa-a73cbac27bfa" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1_abdb5da0-2e0b-4770-b135-e1b75b763efc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment_a1eea5d7-4103-4559-bed6-6116abcc7b41" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_bac5675b-673f-4422-86aa-a73cbac27bfa" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment_a1eea5d7-4103-4559-bed6-6116abcc7b41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_98197865-e5e5-48eb-a6b5-5ac2628b1a84" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_bac5675b-673f-4422-86aa-a73cbac27bfa" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_98197865-e5e5-48eb-a6b5-5ac2628b1a84" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment_26c5f4cc-ba26-4478-a654-0a189e9bdbdf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_bac5675b-673f-4422-86aa-a73cbac27bfa" xlink:to="loc_us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment_26c5f4cc-ba26-4478-a654-0a189e9bdbdf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment_08feff37-ea48-4bc2-9e83-da397d8cc50e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_bac5675b-673f-4422-86aa-a73cbac27bfa" xlink:to="loc_us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment_08feff37-ea48-4bc2-9e83-da397d8cc50e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansAndLeasesReceivableGrossCarryingAmount_982e5ed5-bef8-4e85-91ae-57ca63dec3a1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansAndLeasesReceivableGrossCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_bac5675b-673f-4422-86aa-a73cbac27bfa" xlink:to="loc_us-gaap_LoansAndLeasesReceivableGrossCarryingAmount_982e5ed5-bef8-4e85-91ae-57ca63dec3a1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_bffb03f0-0640-4527-87ea-0971a47b8a38" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_bac5675b-673f-4422-86aa-a73cbac27bfa" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_bffb03f0-0640-4527-87ea-0971a47b8a38" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_481ed895-05a7-4eae-b2a0-a92f21794924" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_bffb03f0-0640-4527-87ea-0971a47b8a38" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_481ed895-05a7-4eae-b2a0-a92f21794924" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_481ed895-05a7-4eae-b2a0-a92f21794924_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_481ed895-05a7-4eae-b2a0-a92f21794924" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_481ed895-05a7-4eae-b2a0-a92f21794924_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_fe9ffe62-f3f4-4d38-9873-516e7ac35ee8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_481ed895-05a7-4eae-b2a0-a92f21794924" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_fe9ffe62-f3f4-4d38-9873-516e7ac35ee8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstateMember_5281352f-93c4-4d8a-a5f2-fb29d2b0b1b9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommercialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_fe9ffe62-f3f4-4d38-9873-516e7ac35ee8" xlink:to="loc_us-gaap_CommercialRealEstateMember_5281352f-93c4-4d8a-a5f2-fb29d2b0b1b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_RealEstateCommercialLandAndDevelopmentMember_126d7316-b2ef-4940-9ff5-d7ca5b757ae7" xlink:href="fsbc-20220930.xsd#fsbc_RealEstateCommercialLandAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_fe9ffe62-f3f4-4d38-9873-516e7ac35ee8" xlink:to="loc_fsbc_RealEstateCommercialLandAndDevelopmentMember_126d7316-b2ef-4940-9ff5-d7ca5b757ae7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_CommercialConstructionLoansMember_cb5582d0-db0e-421b-9b35-244caeb71870" xlink:href="fsbc-20220930.xsd#fsbc_CommercialConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_fe9ffe62-f3f4-4d38-9873-516e7ac35ee8" xlink:to="loc_fsbc_CommercialConstructionLoansMember_cb5582d0-db0e-421b-9b35-244caeb71870" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_ResidentialConstructionLoansMember_27c9d74a-5eaf-4ba2-bcfd-a46dee0fe4af" xlink:href="fsbc-20220930.xsd#fsbc_ResidentialConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_fe9ffe62-f3f4-4d38-9873-516e7ac35ee8" xlink:to="loc_fsbc_ResidentialConstructionLoansMember_27c9d74a-5eaf-4ba2-bcfd-a46dee0fe4af" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialRealEstateMember_8d8aa707-c628-43f2-b5e6-0f4b47c03bdf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResidentialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_fe9ffe62-f3f4-4d38-9873-516e7ac35ee8" xlink:to="loc_us-gaap_ResidentialRealEstateMember_8d8aa707-c628-43f2-b5e6-0f4b47c03bdf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FarmlandMember_f5df246c-3089-403d-9b2f-2cff1d420cb6" xlink:href="fsbc-20220930.xsd#fsbc_FarmlandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_fe9ffe62-f3f4-4d38-9873-516e7ac35ee8" xlink:to="loc_fsbc_FarmlandMember_f5df246c-3089-403d-9b2f-2cff1d420cb6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_1ee8c383-1286-4202-8309-97b5467226c6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_fe9ffe62-f3f4-4d38-9873-516e7ac35ee8" xlink:to="loc_us-gaap_SecuredDebtMember_1ee8c383-1286-4202-8309-97b5467226c6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_8c0398ca-2ba6-4f9d-b851-21ccf6382d32" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_fe9ffe62-f3f4-4d38-9873-516e7ac35ee8" xlink:to="loc_us-gaap_UnsecuredDebtMember_8c0398ca-2ba6-4f9d-b851-21ccf6382d32" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_CommercialPaycheckProtectionProgramMember_05629307-c506-422c-bb5a-e42e62d35f06" xlink:href="fsbc-20220930.xsd#fsbc_CommercialPaycheckProtectionProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_fe9ffe62-f3f4-4d38-9873-516e7ac35ee8" xlink:to="loc_fsbc_CommercialPaycheckProtectionProgramMember_05629307-c506-422c-bb5a-e42e62d35f06" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_02c9237f-e6aa-4744-acc4-102bc91bf75d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_fe9ffe62-f3f4-4d38-9873-516e7ac35ee8" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_02c9237f-e6aa-4744-acc4-102bc91bf75d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnallocatedFinancingReceivablesMember_d9de07d4-3272-457e-b493-4e3b83a156a6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnallocatedFinancingReceivablesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_fe9ffe62-f3f4-4d38-9873-516e7ac35ee8" xlink:to="loc_us-gaap_UnallocatedFinancingReceivablesMember_d9de07d4-3272-457e-b493-4e3b83a156a6" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/InterestBearingDepositsCompositionofNetworkDepositsDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#InterestBearingDepositsCompositionofNetworkDepositsDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/InterestBearingDepositsCompositionofNetworkDepositsDetails" xlink:type="extended" id="i6db39583439a4dfe880bc5e8bf9c9d27_InterestBearingDepositsCompositionofNetworkDepositsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_InterestBearingDepositsLineItems_fa3a2dd9-abae-4ea5-a04d-7c23ce187a59" xlink:href="fsbc-20220930.xsd#fsbc_InterestBearingDepositsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_NetworkDeposits_88aa3165-7238-4939-bf97-a5a0a67e8dce" xlink:href="fsbc-20220930.xsd#fsbc_NetworkDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsbc_InterestBearingDepositsLineItems_fa3a2dd9-abae-4ea5-a04d-7c23ce187a59" xlink:to="loc_fsbc_NetworkDeposits_88aa3165-7238-4939-bf97-a5a0a67e8dce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_InterestBearingDepositsTable_9104c0c4-0f00-4aeb-9812-106c335ee6cd" xlink:href="fsbc-20220930.xsd#fsbc_InterestBearingDepositsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_fsbc_InterestBearingDepositsLineItems_fa3a2dd9-abae-4ea5-a04d-7c23ce187a59" xlink:to="loc_fsbc_InterestBearingDepositsTable_9104c0c4-0f00-4aeb-9812-106c335ee6cd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_8b8df819-c974-41e0-a44d-9a0ee227d921" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_fsbc_InterestBearingDepositsTable_9104c0c4-0f00-4aeb-9812-106c335ee6cd" xlink:to="loc_srt_ProductOrServiceAxis_8b8df819-c974-41e0-a44d-9a0ee227d921" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_8b8df819-c974-41e0-a44d-9a0ee227d921_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_8b8df819-c974-41e0-a44d-9a0ee227d921" xlink:to="loc_srt_ProductsAndServicesDomain_8b8df819-c974-41e0-a44d-9a0ee227d921_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_71cd43ce-1ef1-4ea0-92ac-f33160335624" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_8b8df819-c974-41e0-a44d-9a0ee227d921" xlink:to="loc_srt_ProductsAndServicesDomain_71cd43ce-1ef1-4ea0-92ac-f33160335624" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_CDARSMember_6d28b350-f49f-4856-a7ca-966de7359bc6" xlink:href="fsbc-20220930.xsd#fsbc_CDARSMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_71cd43ce-1ef1-4ea0-92ac-f33160335624" xlink:to="loc_fsbc_CDARSMember_6d28b350-f49f-4856-a7ca-966de7359bc6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_ICSMember_8b46b334-ed32-470b-bd26-53758b993f46" xlink:href="fsbc-20220930.xsd#fsbc_ICSMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_71cd43ce-1ef1-4ea0-92ac-f33160335624" xlink:to="loc_fsbc_ICSMember_8b46b334-ed32-470b-bd26-53758b993f46" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/LeasesNarrativeDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#LeasesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/LeasesNarrativeDetails" xlink:type="extended" id="i5b2425d4544b476bb666801966df042d_LeasesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_e615576a-7a65-49b4-9bea-f33ab684460d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_a2ec46b0-bc8e-4ce6-916b-50cab3cb6a5e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e615576a-7a65-49b4-9bea-f33ab684460d" xlink:to="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_a2ec46b0-bc8e-4ce6-916b-50cab3cb6a5e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseExpense_91270c6d-4093-47c3-bc30-a0a91b8e3186" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e615576a-7a65-49b4-9bea-f33ab684460d" xlink:to="loc_us-gaap_OperatingLeaseExpense_91270c6d-4093-47c3-bc30-a0a91b8e3186" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseAndRentalExpense_c1e919b2-07cd-4f30-a8a9-3a603e5ad778" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LeaseAndRentalExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e615576a-7a65-49b4-9bea-f33ab684460d" xlink:to="loc_us-gaap_LeaseAndRentalExpense_c1e919b2-07cd-4f30-a8a9-3a603e5ad778" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLeaseIncome_76027fe1-b3e0-4d2e-a94a-1b9de5b4ef92" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseLeaseIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e615576a-7a65-49b4-9bea-f33ab684460d" xlink:to="loc_us-gaap_OperatingLeaseLeaseIncome_76027fe1-b3e0-4d2e-a94a-1b9de5b4ef92" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_94173bfd-75e9-4ee4-ae76-14800c83a7f0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e615576a-7a65-49b4-9bea-f33ab684460d" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_94173bfd-75e9-4ee4-ae76-14800c83a7f0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_a5c9fbb2-a61d-4341-b08d-bcfdbf69b786" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_94173bfd-75e9-4ee4-ae76-14800c83a7f0" xlink:to="loc_srt_RangeAxis_a5c9fbb2-a61d-4341-b08d-bcfdbf69b786" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_a5c9fbb2-a61d-4341-b08d-bcfdbf69b786_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_a5c9fbb2-a61d-4341-b08d-bcfdbf69b786" xlink:to="loc_srt_RangeMember_a5c9fbb2-a61d-4341-b08d-bcfdbf69b786_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_33af1993-45b8-48f1-aeee-40eb28ac543a" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_a5c9fbb2-a61d-4341-b08d-bcfdbf69b786" xlink:to="loc_srt_RangeMember_33af1993-45b8-48f1-aeee-40eb28ac543a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_d8c62fb2-0d65-4304-aab9-fed9a51c2bd0" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_33af1993-45b8-48f1-aeee-40eb28ac543a" xlink:to="loc_srt_MinimumMember_d8c62fb2-0d65-4304-aab9-fed9a51c2bd0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_ca54fff5-65ab-479e-9ed5-f91ff46512f8" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_33af1993-45b8-48f1-aeee-40eb28ac543a" xlink:to="loc_srt_MaximumMember_ca54fff5-65ab-479e-9ed5-f91ff46512f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_b65bb922-5a96-4a91-84e3-46a5e76eb388" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_94173bfd-75e9-4ee4-ae76-14800c83a7f0" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_b65bb922-5a96-4a91-84e3-46a5e76eb388" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember_b65bb922-5a96-4a91-84e3-46a5e76eb388_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_b65bb922-5a96-4a91-84e3-46a5e76eb388" xlink:to="loc_us-gaap_TypeOfAdoptionMember_b65bb922-5a96-4a91-84e3-46a5e76eb388_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember_9f32cd24-099a-4536-b113-9f78c86517da" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_b65bb922-5a96-4a91-84e3-46a5e76eb388" xlink:to="loc_us-gaap_TypeOfAdoptionMember_9f32cd24-099a-4536-b113-9f78c86517da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountingStandardsUpdate201602Member_cf7baecf-90d0-4a74-95bf-280d393d46cd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountingStandardsUpdate201602Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_9f32cd24-099a-4536-b113-9f78c86517da" xlink:to="loc_us-gaap_AccountingStandardsUpdate201602Member_cf7baecf-90d0-4a74-95bf-280d393d46cd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_56d27071-a59e-4019-a51d-813a92e3b12e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_94173bfd-75e9-4ee4-ae76-14800c83a7f0" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_56d27071-a59e-4019-a51d-813a92e3b12e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_56d27071-a59e-4019-a51d-813a92e3b12e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_56d27071-a59e-4019-a51d-813a92e3b12e" xlink:to="loc_us-gaap_RelatedPartyDomain_56d27071-a59e-4019-a51d-813a92e3b12e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_a3b29d1a-d391-450c-ae67-b90dcdec09e2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_56d27071-a59e-4019-a51d-813a92e3b12e" xlink:to="loc_us-gaap_RelatedPartyDomain_a3b29d1a-d391-450c-ae67-b90dcdec09e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AffiliatedEntityMember_9f345eea-2508-480b-9842-a5c691fb27b1" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_AffiliatedEntityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_a3b29d1a-d391-450c-ae67-b90dcdec09e2" xlink:to="loc_srt_AffiliatedEntityMember_9f345eea-2508-480b-9842-a5c691fb27b1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/LongTermDebtandOtherBorrowingsDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#LongTermDebtandOtherBorrowingsDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/LongTermDebtandOtherBorrowingsDetails" xlink:type="extended" id="idc19211f790f4b74843ab855a07a3fe6_LongTermDebtandOtherBorrowingsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedDebt_cb3ea97e-6660-4d51-aef5-15a2705b9d93" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubordinatedDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_us-gaap_SubordinatedDebt_cb3ea97e-6660-4d51-aef5-15a2705b9d93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_40893f81-eb5b-4c70-8d29-d6f50d36fcc7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_40893f81-eb5b-4c70-8d29-d6f50d36fcc7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedBorrowingInterestRate_2f7fbbce-6df3-47fa-9b6c-af16ede3b25e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubordinatedBorrowingInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_us-gaap_SubordinatedBorrowingInterestRate_2f7fbbce-6df3-47fa-9b6c-af16ede3b25e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_c6838f3a-9f5d-4e70-825c-348ce888ade8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_c6838f3a-9f5d-4e70-825c-348ce888ade8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_DebtInstrumentFloatingInterestRate_669216bc-3961-47d6-a727-2c2810d44bf3" xlink:href="fsbc-20220930.xsd#fsbc_DebtInstrumentFloatingInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_fsbc_DebtInstrumentFloatingInterestRate_669216bc-3961-47d6-a727-2c2810d44bf3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_NumberOfExistingAndFormerBoardOfDirectors_9207ea2f-d252-4dcb-ad74-8a143942b498" xlink:href="fsbc-20220930.xsd#fsbc_NumberOfExistingAndFormerBoardOfDirectors"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_fsbc_NumberOfExistingAndFormerBoardOfDirectors_9207ea2f-d252-4dcb-ad74-8a143942b498" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_NumberOfShareholders_80dd7bbe-d89b-4521-bb38-f5dde5285475" xlink:href="fsbc-20220930.xsd#fsbc_NumberOfShareholders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_fsbc_NumberOfShareholders_80dd7bbe-d89b-4521-bb38-f5dde5285475" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_b186fa32-c9a1-4b51-a235-7f04685dac93" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_b186fa32-c9a1-4b51-a235-7f04685dac93" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedAmortizationDeferredFinanceCosts_497cd156-99f2-411f-9cec-3fae53b1e945" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedAmortizationDeferredFinanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_us-gaap_AccumulatedAmortizationDeferredFinanceCosts_497cd156-99f2-411f-9cec-3fae53b1e945" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_4d2ee635-6685-4ceb-8e07-92a0a20dde34" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_4d2ee635-6685-4ceb-8e07-92a0a20dde34" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_54bb5e71-808b-4358-b5f5-94a5cef0b5bd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_us-gaap_LineOfCredit_54bb5e71-808b-4358-b5f5-94a5cef0b5bd" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_3e50c6b3-82f8-488a-9546-0f64cdd260c2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_3e50c6b3-82f8-488a-9546-0f64cdd260c2" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_5a274958-52b2-4c89-ba3f-7b1f5203b504" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_5a274958-52b2-4c89-ba3f-7b1f5203b504" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_NumberOfUnsecuredFederalFunds_08f2d72d-6ed7-49b5-bb66-e8ec636ae0ca" xlink:href="fsbc-20220930.xsd#fsbc_NumberOfUnsecuredFederalFunds"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_fsbc_NumberOfUnsecuredFederalFunds_08f2d72d-6ed7-49b5-bb66-e8ec636ae0ca" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_NumberOfCorrespondentBanks_08b5e9f3-a5d2-4247-9d44-abeb14b4df54" xlink:href="fsbc-20220930.xsd#fsbc_NumberOfCorrespondentBanks"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_fsbc_NumberOfCorrespondentBanks_08b5e9f3-a5d2-4247-9d44-abeb14b4df54" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_NumberOfUnsecuredFederalFundsIncreased_799adf04-1af8-48ed-b880-f2e33afa6d02" xlink:href="fsbc-20220930.xsd#fsbc_NumberOfUnsecuredFederalFundsIncreased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_fsbc_NumberOfUnsecuredFederalFundsIncreased_799adf04-1af8-48ed-b880-f2e33afa6d02" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityIncreaseDecreaseForPeriodNet_82d32e3c-d4ca-4bd3-b2b0-6b214ad3c549" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LineOfCreditFacilityIncreaseDecreaseForPeriodNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_us-gaap_LineOfCreditFacilityIncreaseDecreaseForPeriodNet_82d32e3c-d4ca-4bd3-b2b0-6b214ad3c549" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding_13e346d6-416e-4506-8dc4-481cf1d0a08c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding_13e346d6-416e-4506-8dc4-481cf1d0a08c" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_9a00c238-65ef-40d8-9783-4af3aea4e4c2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bf9a523e-81c3-490c-94f8-ad21f50184c0" xlink:to="loc_us-gaap_DebtInstrumentTable_9a00c238-65ef-40d8-9783-4af3aea4e4c2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_90933529-79fd-42de-bb95-8b54c59dc652" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_9a00c238-65ef-40d8-9783-4af3aea4e4c2" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_90933529-79fd-42de-bb95-8b54c59dc652" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_90933529-79fd-42de-bb95-8b54c59dc652_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_90933529-79fd-42de-bb95-8b54c59dc652" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_90933529-79fd-42de-bb95-8b54c59dc652_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_39d8826c-f884-44d7-a48f-96d0f9ce716f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_90933529-79fd-42de-bb95-8b54c59dc652" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_39d8826c-f884-44d7-a48f-96d0f9ce716f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedDebtMember_7f52f142-d049-4ac8-86ee-70fab95d783d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubordinatedDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_39d8826c-f884-44d7-a48f-96d0f9ce716f" xlink:to="loc_us-gaap_SubordinatedDebtMember_7f52f142-d049-4ac8-86ee-70fab95d783d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_063bcec6-e0be-4578-bf0e-a0aa1d97fa2a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_39d8826c-f884-44d7-a48f-96d0f9ce716f" xlink:to="loc_us-gaap_LetterOfCreditMember_063bcec6-e0be-4578-bf0e-a0aa1d97fa2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_b313b145-621c-4434-9efd-1829928d4fd1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_39d8826c-f884-44d7-a48f-96d0f9ce716f" xlink:to="loc_us-gaap_LineOfCreditMember_b313b145-621c-4434-9efd-1829928d4fd1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_86223cda-76f1-4b90-bea0-c78cfd3f693b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_9a00c238-65ef-40d8-9783-4af3aea4e4c2" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_86223cda-76f1-4b90-bea0-c78cfd3f693b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_86223cda-76f1-4b90-bea0-c78cfd3f693b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_86223cda-76f1-4b90-bea0-c78cfd3f693b" xlink:to="loc_us-gaap_RelatedPartyDomain_86223cda-76f1-4b90-bea0-c78cfd3f693b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_c896f9c9-f4e7-4593-ae40-a1df5a51b5f1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_86223cda-76f1-4b90-bea0-c78cfd3f693b" xlink:to="loc_us-gaap_RelatedPartyDomain_c896f9c9-f4e7-4593-ae40-a1df5a51b5f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_EntityControlledByMemberOfBoardOfDirectorsAndThreeShareholdersMember_935dff42-b436-4fc7-9f8d-be99d9bd4905" xlink:href="fsbc-20220930.xsd#fsbc_EntityControlledByMemberOfBoardOfDirectorsAndThreeShareholdersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_c896f9c9-f4e7-4593-ae40-a1df5a51b5f1" xlink:to="loc_fsbc_EntityControlledByMemberOfBoardOfDirectorsAndThreeShareholdersMember_935dff42-b436-4fc7-9f8d-be99d9bd4905" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_f25217b5-9467-4e1c-93e6-6ea9b04af757" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_9a00c238-65ef-40d8-9783-4af3aea4e4c2" xlink:to="loc_us-gaap_DebtInstrumentAxis_f25217b5-9467-4e1c-93e6-6ea9b04af757" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_f25217b5-9467-4e1c-93e6-6ea9b04af757_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_f25217b5-9467-4e1c-93e6-6ea9b04af757" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_f25217b5-9467-4e1c-93e6-6ea9b04af757_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_10253de8-92f5-4bf3-ac01-859e1e851fcf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_f25217b5-9467-4e1c-93e6-6ea9b04af757" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_10253de8-92f5-4bf3-ac01-859e1e851fcf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FixedToFloatingRateSubordinatedNotesIssuedNov2019Member_01a058ab-2d61-4c35-b359-5767d05ff777" xlink:href="fsbc-20220930.xsd#fsbc_FixedToFloatingRateSubordinatedNotesIssuedNov2019Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_10253de8-92f5-4bf3-ac01-859e1e851fcf" xlink:to="loc_fsbc_FixedToFloatingRateSubordinatedNotesIssuedNov2019Member_01a058ab-2d61-4c35-b359-5767d05ff777" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FixedToFloatingRateSubordinatedNotesIssuedSep2017Member_3286c3a6-ffaa-42d0-94b0-3448884153ca" xlink:href="fsbc-20220930.xsd#fsbc_FixedToFloatingRateSubordinatedNotesIssuedSep2017Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_10253de8-92f5-4bf3-ac01-859e1e851fcf" xlink:to="loc_fsbc_FixedToFloatingRateSubordinatedNotesIssuedSep2017Member_3286c3a6-ffaa-42d0-94b0-3448884153ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_EntityControlledByMemberOfBoardOfDirectorsAndThreeShareholdersMember_ef14ff42-c088-43c5-b3a5-b4ad1f61b754" xlink:href="fsbc-20220930.xsd#fsbc_EntityControlledByMemberOfBoardOfDirectorsAndThreeShareholdersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_10253de8-92f5-4bf3-ac01-859e1e851fcf" xlink:to="loc_fsbc_EntityControlledByMemberOfBoardOfDirectorsAndThreeShareholdersMember_ef14ff42-c088-43c5-b3a5-b4ad1f61b754" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_SubordinatedNotesIssuedSep2017Member_fb181f53-6ed2-47ce-a8c4-2f99f5dabaa4" xlink:href="fsbc-20220930.xsd#fsbc_SubordinatedNotesIssuedSep2017Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_10253de8-92f5-4bf3-ac01-859e1e851fcf" xlink:to="loc_fsbc_SubordinatedNotesIssuedSep2017Member_fb181f53-6ed2-47ce-a8c4-2f99f5dabaa4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_LettersOfCreditPledgedAsSecurityForStateOfCaliforniaDepositsMember_77d9c890-237c-4799-957f-777b5caeb8db" xlink:href="fsbc-20220930.xsd#fsbc_LettersOfCreditPledgedAsSecurityForStateOfCaliforniaDepositsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_10253de8-92f5-4bf3-ac01-859e1e851fcf" xlink:to="loc_fsbc_LettersOfCreditPledgedAsSecurityForStateOfCaliforniaDepositsMember_77d9c890-237c-4799-957f-777b5caeb8db" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_SecureLocalAgencyDepositMember_93147fd9-e850-479f-83bf-716d5528ccd0" xlink:href="fsbc-20220930.xsd#fsbc_SecureLocalAgencyDepositMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_10253de8-92f5-4bf3-ac01-859e1e851fcf" xlink:to="loc_fsbc_SecureLocalAgencyDepositMember_93147fd9-e850-479f-83bf-716d5528ccd0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FederalReserveDiscountWindowMember_0680a2a0-fc1f-4d95-8038-95d79a20e4cd" xlink:href="fsbc-20220930.xsd#fsbc_FederalReserveDiscountWindowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_10253de8-92f5-4bf3-ac01-859e1e851fcf" xlink:to="loc_fsbc_FederalReserveDiscountWindowMember_0680a2a0-fc1f-4d95-8038-95d79a20e4cd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FHLBAgreementMember_90aaa616-329d-4813-a5a3-ee7020f61aea" xlink:href="fsbc-20220930.xsd#fsbc_FHLBAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_10253de8-92f5-4bf3-ac01-859e1e851fcf" xlink:to="loc_fsbc_FHLBAgreementMember_90aaa616-329d-4813-a5a3-ee7020f61aea" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FixedToFloatingRateSubordinatedNotesIssuedAugust2022Member_78cc02ce-e10c-493d-80fc-6874c7130ea0" xlink:href="fsbc-20220930.xsd#fsbc_FixedToFloatingRateSubordinatedNotesIssuedAugust2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_10253de8-92f5-4bf3-ac01-859e1e851fcf" xlink:to="loc_fsbc_FixedToFloatingRateSubordinatedNotesIssuedAugust2022Member_78cc02ce-e10c-493d-80fc-6874c7130ea0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_EntityControlledByExistingAndFormerBoardMembersAndAffiliatesMember_42a860c0-5b23-4f12-908d-ef36e47a7b8f" xlink:href="fsbc-20220930.xsd#fsbc_EntityControlledByExistingAndFormerBoardMembersAndAffiliatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_10253de8-92f5-4bf3-ac01-859e1e851fcf" xlink:to="loc_fsbc_EntityControlledByExistingAndFormerBoardMembersAndAffiliatesMember_42a860c0-5b23-4f12-908d-ef36e47a7b8f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_FiveUnsecuredFederalFundsLineOfCreditMember_98746987-25da-4d17-b07b-eed1ff059f9f" xlink:href="fsbc-20220930.xsd#fsbc_FiveUnsecuredFederalFundsLineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_10253de8-92f5-4bf3-ac01-859e1e851fcf" xlink:to="loc_fsbc_FiveUnsecuredFederalFundsLineOfCreditMember_98746987-25da-4d17-b07b-eed1ff059f9f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_OneUnsecuredFederalFundsLineOfCreditMember_240efbf4-43e6-4d7c-ba6a-3742c8c5c72f" xlink:href="fsbc-20220930.xsd#fsbc_OneUnsecuredFederalFundsLineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_10253de8-92f5-4bf3-ac01-859e1e851fcf" xlink:to="loc_fsbc_OneUnsecuredFederalFundsLineOfCreditMember_240efbf4-43e6-4d7c-ba6a-3742c8c5c72f" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_SixUnsecuredFederalFundsLineOfCreditMember_1ec0a3ba-97fe-48dc-b037-6973c7db48fc" xlink:href="fsbc-20220930.xsd#fsbc_SixUnsecuredFederalFundsLineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_10253de8-92f5-4bf3-ac01-859e1e851fcf" xlink:to="loc_fsbc_SixUnsecuredFederalFundsLineOfCreditMember_1ec0a3ba-97fe-48dc-b037-6973c7db48fc" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_fa0654fd-d035-4c40-a3a3-6716b16df384" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_9a00c238-65ef-40d8-9783-4af3aea4e4c2" xlink:to="loc_us-gaap_VariableRateAxis_fa0654fd-d035-4c40-a3a3-6716b16df384" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_fa0654fd-d035-4c40-a3a3-6716b16df384_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_fa0654fd-d035-4c40-a3a3-6716b16df384" xlink:to="loc_us-gaap_VariableRateDomain_fa0654fd-d035-4c40-a3a3-6716b16df384_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_70ef8833-5bb1-4f4e-9f6a-30e14932e162" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_fa0654fd-d035-4c40-a3a3-6716b16df384" xlink:to="loc_us-gaap_VariableRateDomain_70ef8833-5bb1-4f4e-9f6a-30e14932e162" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_1c92f4a4-3506-4877-aa08-86bef2cd86cc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_70ef8833-5bb1-4f4e-9f6a-30e14932e162" xlink:to="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_1c92f4a4-3506-4877-aa08-86bef2cd86cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_b171d6a4-a2a8-4c93-8080-9b189a000ca2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_70ef8833-5bb1-4f4e-9f6a-30e14932e162" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_b171d6a4-a2a8-4c93-8080-9b189a000ca2" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/ShareholdersEquityNarrativeDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#ShareholdersEquityNarrativeDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/ShareholdersEquityNarrativeDetails" xlink:type="extended" id="i3d4535a8118944089d99487193b89473_ShareholdersEquityNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b4eaa0e1-a1bc-4bea-8365-4e32e86252f6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_44ee390e-2b97-4ff0-ac68-e3398bf8292d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b4eaa0e1-a1bc-4bea-8365-4e32e86252f6" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_44ee390e-2b97-4ff0-ac68-e3398bf8292d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_15010cbf-1c8f-4aa1-b796-0e28afe6e320" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DividendsPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b4eaa0e1-a1bc-4bea-8365-4e32e86252f6" xlink:to="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_15010cbf-1c8f-4aa1-b796-0e28afe6e320" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_3839aec9-67c3-45b7-af20-2901a6294b8f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b4eaa0e1-a1bc-4bea-8365-4e32e86252f6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_3839aec9-67c3-45b7-af20-2901a6294b8f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_b3018977-2903-4063-8507-59cfbec8f03c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b4eaa0e1-a1bc-4bea-8365-4e32e86252f6" xlink:to="loc_us-gaap_ShareBasedCompensation_b3018977-2903-4063-8507-59cfbec8f03c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_UnvestedRestrictedShares_e45fddbb-25b9-46f3-9633-dbc891ed5a57" xlink:href="fsbc-20220930.xsd#fsbc_UnvestedRestrictedShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b4eaa0e1-a1bc-4bea-8365-4e32e86252f6" xlink:to="loc_fsbc_UnvestedRestrictedShares_e45fddbb-25b9-46f3-9633-dbc891ed5a57" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeBenefitsAndShareBasedCompensation_cbacc845-e058-4132-946c-04751c276577" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeBenefitsAndShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b4eaa0e1-a1bc-4bea-8365-4e32e86252f6" xlink:to="loc_us-gaap_EmployeeBenefitsAndShareBasedCompensation_cbacc845-e058-4132-946c-04751c276577" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2c8296fd-2903-4ae0-b46f-420fbe9e334d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b4eaa0e1-a1bc-4bea-8365-4e32e86252f6" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2c8296fd-2903-4ae0-b46f-420fbe9e334d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusAxis_5c33d464-e9a5-475a-9eb4-b2048db4599a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GranteeStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2c8296fd-2903-4ae0-b46f-420fbe9e334d" xlink:to="loc_us-gaap_GranteeStatusAxis_5c33d464-e9a5-475a-9eb4-b2048db4599a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_5c33d464-e9a5-475a-9eb4-b2048db4599a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GranteeStatusAxis_5c33d464-e9a5-475a-9eb4-b2048db4599a" xlink:to="loc_us-gaap_GranteeStatusDomain_5c33d464-e9a5-475a-9eb4-b2048db4599a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_11d6183d-b6fb-4039-aa42-b92b57aedb8c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GranteeStatusAxis_5c33d464-e9a5-475a-9eb4-b2048db4599a" xlink:to="loc_us-gaap_GranteeStatusDomain_11d6183d-b6fb-4039-aa42-b92b57aedb8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_0914eb77-740f-498a-9b9f-cecae14ad1e7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedPaymentArrangementEmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_11d6183d-b6fb-4039-aa42-b92b57aedb8c" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_0914eb77-740f-498a-9b9f-cecae14ad1e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_ShareBasedPaymentArrangementExecutivesAndDirectorsMember_2089099b-9230-4c94-8624-fa67f2f09a9b" xlink:href="fsbc-20220930.xsd#fsbc_ShareBasedPaymentArrangementExecutivesAndDirectorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_11d6183d-b6fb-4039-aa42-b92b57aedb8c" xlink:to="loc_fsbc_ShareBasedPaymentArrangementExecutivesAndDirectorsMember_2089099b-9230-4c94-8624-fa67f2f09a9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_a9eda84f-9555-4cf5-a3f9-c4d1534b4922" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2c8296fd-2903-4ae0-b46f-420fbe9e334d" xlink:to="loc_srt_RangeAxis_a9eda84f-9555-4cf5-a3f9-c4d1534b4922" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_a9eda84f-9555-4cf5-a3f9-c4d1534b4922_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_a9eda84f-9555-4cf5-a3f9-c4d1534b4922" xlink:to="loc_srt_RangeMember_a9eda84f-9555-4cf5-a3f9-c4d1534b4922_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_9fca3614-7fd6-4793-9ae5-4d9c66f50f27" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_a9eda84f-9555-4cf5-a3f9-c4d1534b4922" xlink:to="loc_srt_RangeMember_9fca3614-7fd6-4793-9ae5-4d9c66f50f27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_c0244db9-0692-4e40-ae2e-7199ac0b9ad2" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_9fca3614-7fd6-4793-9ae5-4d9c66f50f27" xlink:to="loc_srt_MinimumMember_c0244db9-0692-4e40-ae2e-7199ac0b9ad2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_e87bba27-c6cf-420a-aeb4-9d90a145ea8a" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_9fca3614-7fd6-4793-9ae5-4d9c66f50f27" xlink:to="loc_srt_MaximumMember_e87bba27-c6cf-420a-aeb4-9d90a145ea8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_9c24c090-6344-4240-b6df-f5a89369231e" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2c8296fd-2903-4ae0-b46f-420fbe9e334d" xlink:to="loc_srt_TitleOfIndividualAxis_9c24c090-6344-4240-b6df-f5a89369231e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_9c24c090-6344-4240-b6df-f5a89369231e_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_9c24c090-6344-4240-b6df-f5a89369231e" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_9c24c090-6344-4240-b6df-f5a89369231e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_5e2c8b3c-febc-4444-9f4a-356909e3c03c" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_9c24c090-6344-4240-b6df-f5a89369231e" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_5e2c8b3c-febc-4444-9f4a-356909e3c03c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OfficerMember_6764a9c0-864c-4451-bd41-b256179c4f2c" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_OfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_5e2c8b3c-febc-4444-9f4a-356909e3c03c" xlink:to="loc_srt_OfficerMember_6764a9c0-864c-4451-bd41-b256179c4f2c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ExecutiveOfficerMember_b4005fcc-ef9f-4289-a05d-fa01f7711af9" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ExecutiveOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_5e2c8b3c-febc-4444-9f4a-356909e3c03c" xlink:to="loc_srt_ExecutiveOfficerMember_b4005fcc-ef9f-4289-a05d-fa01f7711af9" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/ShareholdersEquitySummaryofUnvestedSharesActivityDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#ShareholdersEquitySummaryofUnvestedSharesActivityDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/ShareholdersEquitySummaryofUnvestedSharesActivityDetails" xlink:type="extended" id="i0434a51fa570410bbd2792b737fea430_ShareholdersEquitySummaryofUnvestedSharesActivityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e17370ac-42b9-4524-9cd7-7c53a83dcb6c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_83a90ed3-eb73-4a2c-93e1-1d1693419283" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e17370ac-42b9-4524-9cd7-7c53a83dcb6c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_83a90ed3-eb73-4a2c-93e1-1d1693419283" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_1c4213c9-ee6b-446e-b22e-0c73df6428a4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_83a90ed3-eb73-4a2c-93e1-1d1693419283" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_1c4213c9-ee6b-446e-b22e-0c73df6428a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_8c0d53f3-b65f-4629-8952-c187bd2b08f5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_83a90ed3-eb73-4a2c-93e1-1d1693419283" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_8c0d53f3-b65f-4629-8952-c187bd2b08f5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_e4415659-2dc1-4855-bb0e-2c6fa0b45421" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_83a90ed3-eb73-4a2c-93e1-1d1693419283" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_e4415659-2dc1-4855-bb0e-2c6fa0b45421" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_10fa2074-8021-41d7-bd7e-70a9a56d11fe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_83a90ed3-eb73-4a2c-93e1-1d1693419283" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_10fa2074-8021-41d7-bd7e-70a9a56d11fe" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_e0ca310a-dcce-4e0d-a929-cd9b745463d6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cec5a7e7-ba8c-4ee4-aee5-210dfb6f0b48" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e17370ac-42b9-4524-9cd7-7c53a83dcb6c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cec5a7e7-ba8c-4ee4-aee5-210dfb6f0b48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_20fb0a08-27f2-40fb-9ea2-9998fa77d6f6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cec5a7e7-ba8c-4ee4-aee5-210dfb6f0b48" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_20fb0a08-27f2-40fb-9ea2-9998fa77d6f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_4948fc27-8ddd-4d1c-a4fb-b0ed709bb1b6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cec5a7e7-ba8c-4ee4-aee5-210dfb6f0b48" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_4948fc27-8ddd-4d1c-a4fb-b0ed709bb1b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_3ff11a50-1052-48b1-a1f3-0a7ede474222" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cec5a7e7-ba8c-4ee4-aee5-210dfb6f0b48" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_3ff11a50-1052-48b1-a1f3-0a7ede474222" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_e24dbb54-7e6b-4711-a98f-26482b910b61" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cec5a7e7-ba8c-4ee4-aee5-210dfb6f0b48" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_e24dbb54-7e6b-4711-a98f-26482b910b61" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_8310949a-6501-40a1-8dcd-829ff8cb358a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4b578e91-25a1-4049-b755-5ac2c590027a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e17370ac-42b9-4524-9cd7-7c53a83dcb6c" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4b578e91-25a1-4049-b755-5ac2c590027a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_badbf196-1391-4a53-88b7-9a27fcedce85" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4b578e91-25a1-4049-b755-5ac2c590027a" xlink:to="loc_us-gaap_AwardTypeAxis_badbf196-1391-4a53-88b7-9a27fcedce85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_badbf196-1391-4a53-88b7-9a27fcedce85_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_badbf196-1391-4a53-88b7-9a27fcedce85" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_badbf196-1391-4a53-88b7-9a27fcedce85_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d5a26380-9deb-4e9c-92c5-bdcd3ffaed58" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_badbf196-1391-4a53-88b7-9a27fcedce85" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d5a26380-9deb-4e9c-92c5-bdcd3ffaed58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_732e471d-fbd6-40af-ad01-3d5e92d44e3b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d5a26380-9deb-4e9c-92c5-bdcd3ffaed58" xlink:to="loc_us-gaap_RestrictedStockMember_732e471d-fbd6-40af-ad01-3d5e92d44e3b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/CommitmentsandContingenciesUnfundedLoanCommitmentsandStandbyLettersofCreditDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#CommitmentsandContingenciesUnfundedLoanCommitmentsandStandbyLettersofCreditDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/CommitmentsandContingenciesUnfundedLoanCommitmentsandStandbyLettersofCreditDetails" xlink:type="extended" id="i5d87dddfabff40f79aaf432c288aa9ae_CommitmentsandContingenciesUnfundedLoanCommitmentsandStandbyLettersofCreditDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_923e12cf-6ba3-409b-8d48-60ec0ab33dd3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitment_f7186f74-726e-48e2-b7f0-2783f47cc46d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherCommitment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_923e12cf-6ba3-409b-8d48-60ec0ab33dd3" xlink:to="loc_us-gaap_OtherCommitment_f7186f74-726e-48e2-b7f0-2783f47cc46d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_cd723b8d-ba50-4c08-a50d-6113905ea8db" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_923e12cf-6ba3-409b-8d48-60ec0ab33dd3" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_cd723b8d-ba50-4c08-a50d-6113905ea8db" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsAxis_71c44321-3ebe-4191-a4d0-c3aa723f2b6d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherCommitmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_cd723b8d-ba50-4c08-a50d-6113905ea8db" xlink:to="loc_us-gaap_OtherCommitmentsAxis_71c44321-3ebe-4191-a4d0-c3aa723f2b6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsDomain_71c44321-3ebe-4191-a4d0-c3aa723f2b6d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherCommitmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_OtherCommitmentsAxis_71c44321-3ebe-4191-a4d0-c3aa723f2b6d" xlink:to="loc_us-gaap_OtherCommitmentsDomain_71c44321-3ebe-4191-a4d0-c3aa723f2b6d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsDomain_94faa0b9-1a27-4d90-b8fd-51482147dbc8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherCommitmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_OtherCommitmentsAxis_71c44321-3ebe-4191-a4d0-c3aa723f2b6d" xlink:to="loc_us-gaap_OtherCommitmentsDomain_94faa0b9-1a27-4d90-b8fd-51482147dbc8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_CommercialLinesOfCreditMember_4e6f9ef0-3aa4-45ab-858f-daf61a961cff" xlink:href="fsbc-20220930.xsd#fsbc_CommercialLinesOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsDomain_94faa0b9-1a27-4d90-b8fd-51482147dbc8" xlink:to="loc_fsbc_CommercialLinesOfCreditMember_4e6f9ef0-3aa4-45ab-858f-daf61a961cff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_UndisbursedConstructionLoansMember_ca0425b1-46fd-4d0c-8fcf-905c33c7f12e" xlink:href="fsbc-20220930.xsd#fsbc_UndisbursedConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsDomain_94faa0b9-1a27-4d90-b8fd-51482147dbc8" xlink:to="loc_fsbc_UndisbursedConstructionLoansMember_ca0425b1-46fd-4d0c-8fcf-905c33c7f12e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_UndisbursedCommercialRealEstateLoansMember_72220cc7-e7d5-48c1-8c3a-6d10182c9dc4" xlink:href="fsbc-20220930.xsd#fsbc_UndisbursedCommercialRealEstateLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsDomain_94faa0b9-1a27-4d90-b8fd-51482147dbc8" xlink:to="loc_fsbc_UndisbursedCommercialRealEstateLoansMember_72220cc7-e7d5-48c1-8c3a-6d10182c9dc4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_AgriculturalLinesOfCreditMember_ed533258-e994-45ae-93a9-0a29820127ff" xlink:href="fsbc-20220930.xsd#fsbc_AgriculturalLinesOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsDomain_94faa0b9-1a27-4d90-b8fd-51482147dbc8" xlink:to="loc_fsbc_AgriculturalLinesOfCreditMember_ed533258-e994-45ae-93a9-0a29820127ff" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_UndisbursedAgriculturalRealEstateLoansMember_07fc7722-e9d7-467e-a354-75dc548ec629" xlink:href="fsbc-20220930.xsd#fsbc_UndisbursedAgriculturalRealEstateLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsDomain_94faa0b9-1a27-4d90-b8fd-51482147dbc8" xlink:to="loc_fsbc_UndisbursedAgriculturalRealEstateLoansMember_07fc7722-e9d7-467e-a354-75dc548ec629" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_OtherCommitmentsMember_ba886ad5-d95e-4742-889b-2c14bf183073" xlink:href="fsbc-20220930.xsd#fsbc_OtherCommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsDomain_94faa0b9-1a27-4d90-b8fd-51482147dbc8" xlink:to="loc_fsbc_OtherCommitmentsMember_ba886ad5-d95e-4742-889b-2c14bf183073" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="simple" xlink:href="fsbc-20220930.xsd#CommitmentsandContingenciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="extended" id="id8aa399b73774ed7952315c44b497be1_CommitmentsandContingenciesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsLineItems_bf1bd050-c45c-4825-8786-44f3e3eaea20" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherCommitmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansAndLeasesReceivableAllowance_08a97d21-aaa2-46f9-9fbd-273ec295189a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansAndLeasesReceivableAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_bf1bd050-c45c-4825-8786-44f3e3eaea20" xlink:to="loc_us-gaap_LoansAndLeasesReceivableAllowance_08a97d21-aaa2-46f9-9fbd-273ec295189a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_RealEstateRelatedLoansPercentage_b9d20f0c-3da9-43c8-b2ea-5c5f39fda207" xlink:href="fsbc-20220930.xsd#fsbc_RealEstateRelatedLoansPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_bf1bd050-c45c-4825-8786-44f3e3eaea20" xlink:to="loc_fsbc_RealEstateRelatedLoansPercentage_b9d20f0c-3da9-43c8-b2ea-5c5f39fda207" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_Deposits5MillionOrMoreNumberOfDepositRelationships_5cabf3e3-fc3d-43b4-ba51-65969ef56bea" xlink:href="fsbc-20220930.xsd#fsbc_Deposits5MillionOrMoreNumberOfDepositRelationships"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_bf1bd050-c45c-4825-8786-44f3e3eaea20" xlink:to="loc_fsbc_Deposits5MillionOrMoreNumberOfDepositRelationships_5cabf3e3-fc3d-43b4-ba51-65969ef56bea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_Deposits5MillionOrMorePerDeposit_2786a0c9-3353-442a-aeac-f80503b6bfe0" xlink:href="fsbc-20220930.xsd#fsbc_Deposits5MillionOrMorePerDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_bf1bd050-c45c-4825-8786-44f3e3eaea20" xlink:to="loc_fsbc_Deposits5MillionOrMorePerDeposit_2786a0c9-3353-442a-aeac-f80503b6bfe0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_Deposits5MillionOrMoreAmount_a7d0d598-f544-4a52-99cf-de60f01cef73" xlink:href="fsbc-20220930.xsd#fsbc_Deposits5MillionOrMoreAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_bf1bd050-c45c-4825-8786-44f3e3eaea20" xlink:to="loc_fsbc_Deposits5MillionOrMoreAmount_a7d0d598-f544-4a52-99cf-de60f01cef73" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_PercentageOfDepositsOver5MillionToDeposits_4d073a05-5ea5-4038-911a-951f5f157ecf" xlink:href="fsbc-20220930.xsd#fsbc_PercentageOfDepositsOver5MillionToDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_bf1bd050-c45c-4825-8786-44f3e3eaea20" xlink:to="loc_fsbc_PercentageOfDepositsOver5MillionToDeposits_4d073a05-5ea5-4038-911a-951f5f157ecf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_LargestSingleDeposit_bb444999-8135-487d-a4bf-1b168866a7c1" xlink:href="fsbc-20220930.xsd#fsbc_LargestSingleDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_bf1bd050-c45c-4825-8786-44f3e3eaea20" xlink:to="loc_fsbc_LargestSingleDeposit_bb444999-8135-487d-a4bf-1b168866a7c1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsbc_PercentageOfLargestSingleDepositToDeposits_2ca51bc5-788a-4eee-9955-322d9be598fb" xlink:href="fsbc-20220930.xsd#fsbc_PercentageOfLargestSingleDepositToDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_bf1bd050-c45c-4825-8786-44f3e3eaea20" xlink:to="loc_fsbc_PercentageOfLargestSingleDepositToDeposits_2ca51bc5-788a-4eee-9955-322d9be598fb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashUninsuredAmount_73bac909-4edb-45a4-9bcc-6c4d34a51c01" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashUninsuredAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_bf1bd050-c45c-4825-8786-44f3e3eaea20" xlink:to="loc_us-gaap_CashUninsuredAmount_73bac909-4edb-45a4-9bcc-6c4d34a51c01" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsTable_f3d84031-3066-4a7c-9b0f-12d68429ec15" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherCommitmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_bf1bd050-c45c-4825-8786-44f3e3eaea20" xlink:to="loc_us-gaap_OtherCommitmentsTable_f3d84031-3066-4a7c-9b0f-12d68429ec15" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_46aceb87-acb3-4b67-9535-2932a85d2ad4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_f3d84031-3066-4a7c-9b0f-12d68429ec15" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_46aceb87-acb3-4b67-9535-2932a85d2ad4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_46aceb87-acb3-4b67-9535-2932a85d2ad4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_46aceb87-acb3-4b67-9535-2932a85d2ad4" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_46aceb87-acb3-4b67-9535-2932a85d2ad4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_9f4ca4ce-b494-4888-9bee-a3633bf1b5a4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_46aceb87-acb3-4b67-9535-2932a85d2ad4" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_9f4ca4ce-b494-4888-9bee-a3633bf1b5a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnfundedLoanCommitmentMember_7666228e-c6ff-408a-bb33-87a26730539e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnfundedLoanCommitmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_9f4ca4ce-b494-4888-9bee-a3633bf1b5a4" xlink:to="loc_us-gaap_UnfundedLoanCommitmentMember_7666228e-c6ff-408a-bb33-87a26730539e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fivestarbank.com/role/SubsequentEventsDetailsNarrative" xlink:type="simple" xlink:href="fsbc-20220930.xsd#SubsequentEventsDetailsNarrative"/>
  <link:definitionLink xlink:role="http://fivestarbank.com/role/SubsequentEventsDetailsNarrative" xlink:type="extended" id="if30dc5126c0f4539a2bade7b080e4296_SubsequentEventsDetailsNarrative">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_49f2cce7-140a-44b8-904c-235ca69cc256" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_b0f8022a-a519-4abd-98d1-05bdd6d3e4a2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_49f2cce7-140a-44b8-904c-235ca69cc256" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_b0f8022a-a519-4abd-98d1-05bdd6d3e4a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_b729ea57-a8da-40ac-b629-0f50e66b5326" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DividendsPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_49f2cce7-140a-44b8-904c-235ca69cc256" xlink:to="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_b729ea57-a8da-40ac-b629-0f50e66b5326" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_707ddd9f-a2ae-4be8-a1f0-41edd7503165" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_49f2cce7-140a-44b8-904c-235ca69cc256" xlink:to="loc_us-gaap_SubsequentEventTable_707ddd9f-a2ae-4be8-a1f0-41edd7503165" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_a93a8a34-47bd-4217-913b-803f8af76589" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_707ddd9f-a2ae-4be8-a1f0-41edd7503165" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_a93a8a34-47bd-4217-913b-803f8af76589" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_a93a8a34-47bd-4217-913b-803f8af76589_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_a93a8a34-47bd-4217-913b-803f8af76589" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_a93a8a34-47bd-4217-913b-803f8af76589_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_a3033851-5cd1-4e69-90e2-ea644a71bb67" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_a93a8a34-47bd-4217-913b-803f8af76589" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_a3033851-5cd1-4e69-90e2-ea644a71bb67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_04a5b3fd-86d5-4070-8b53-6070148aed14" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_a3033851-5cd1-4e69-90e2-ea644a71bb67" xlink:to="loc_us-gaap_SubsequentEventMember_04a5b3fd-86d5-4070-8b53-6070148aed14" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
