<?xml version="1.0" encoding="US-ASCII"?>
<!-- Generated by Broadridge Transform (tm) - http://www.broadridge.com -->
<!-- Created: Mon Apr 27 10:05:23 UTC 2026 -->
<linkbase xmlns="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:xbrldt="http://xbrl.org/2005/xbrldt">
  <roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#IndividualsOnly" roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly"/>
  <roleRef xlink:type="simple" xlink:href="uctt-20260522.xsd#uctt_r_AdditionalDimensions" roleURI="http://uct.com/role/AdditionalDimensions"/>
  <arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default"/>
  <arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain"/>
  <arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension"/>
  <arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member"/>
  <arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" arcroleURI="http://xbrl.org/int/dim/arcrole/all"/>
  <definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended">
    <loc xlink:type="locator" xlink:label="ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#ecd_AllIndividualsMember"/>
    <loc xlink:type="locator" xlink:label="uctt_JamesScholhamerMember" xlink:href="uctt-20260522.xsd#uctt_JamesScholhamerMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ecd_AllIndividualsMember" xlink:to="uctt_JamesScholhamerMember" order="2" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:label="uctt_ClarenceGrangerMember" xlink:href="uctt-20260522.xsd#uctt_ClarenceGrangerMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ecd_AllIndividualsMember" xlink:to="uctt_ClarenceGrangerMember" order="4" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:label="uctt_JamesXiaoMember" xlink:href="uctt-20260522.xsd#uctt_JamesXiaoMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ecd_AllIndividualsMember" xlink:to="uctt_JamesXiaoMember" order="6" xbrldt:closed="true"/>
  </definitionLink>
<!-- [WMV7][kIRmVy2+sU+QD+EPpX8lEU2sdEiiqdxCP6ke0qG5UDtZ/4ZLTEpe9V0VayElzXh4i1uoct2HsEqTTj3RYgHLbeBBq6QlntDbATuoksO6yG1/HeCkRxkcj+gNdc7S3UKC+qSp+jCSsYNjHLRVY9sQuLwLzK1n7XLAUqFE+XQGcIUa52JyXb5Q8ZTaxIAHAS6uSTty1ttzYG5tq0/05bePRgkoxeVvZIpgr97Cs/47/NDvLLzSUZmmR7X8Ae7c5hbDJDIY9qtoqWgsGUqQy4VyCtHPLItvZEl6FAkO1NLj6yfI5lC5kIUd1C+P98WDS6T+4P8KzK53qXCieTl5nLr2+JACpu91GUd44/s0diyK8go/RqklC6ZvO1r0dIX2XA==] CSR-->
  <definitionLink xlink:role="http://uct.com/role/AdditionalDimensions" xlink:type="extended"/>
</linkbase>