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Exhibit 31.1

CERTIFICATION

I, James Xiao, certify that:

1. I have reviewed this quarterly report on Form 10-Q/A of Ultra Clean Holdings, Inc.; and

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report.

Date: May 1, 2026
/s/ JAMES XIAO
James Xiao
Chief Executive Officer