8-K

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

On April 13, 2021, Ultra Clean Holdings, Inc. (the “Company”) closed its previously announced registered underwritten public offering of 3,181,818 shares of the Company’s common stock, par value $0.001 per share (the “Common Stock”), pursuant to an underwriting agreement dated April 8, 2021 (the “Underwriting Agreement”) by and between the Company and Needham & Company, LLC as representative of the several underwriters named therein (the “Underwriters”), at a price of $55.00 per share to the public (the “Offering Price Per Share”).

Pursuant to the Underwriting Agreement, the Company granted the Underwriters an option to purchase an additional 477,272 shares of Common Stock (the “Option Shares”) at the Offering Price Per Share, which the Underwriters exercised in full on April 26, 2021. On May 3, 2021, the Company closed the offering of the Option Shares.

The Company received net proceeds from the sale of the Option Shares of approximately $25.2 million, after deducting the underwriting discount.

A copy of the opinion of Davis Polk & Wardwell LLP relating to the validity of the Option Shares is filed as Exhibit 5.1 hereto and is incorporated by reference into the Registration Statement.

(d) Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Exhibit 5.1

Ultra Clean Holdings, Inc.

26462 Corporate Avenue

Hayward, California 94545

Ladies and Gentlemen:

Ultra Clean Holdings, Inc., a Delaware corporation (the “Company”), has filed with the Securities and Exchange Commission a Registration Statement on Form S-3 (File No. 333-255039)(the “RegistrationStatement”) for the purpose of registering under the Securities Act of 1933, as amended (the “Securities Act”), certain securities, including the 477,272 shares of its common stock, par value $0.001 per share (the “Securities”) to be sold pursuant to the Underwriting Agreement dated April 8, 2021 (the “Underwriting Agreement”) among the Company and the several underwriters named therein (the “Underwriters”), with respect to which the Underwriters have exercised their option to purchase. The Securities are in addition to 3,181,818 shares of its common stock, par value $0.001 per share previously sold pursuant to the Underwriting Agreement.

We, as your counsel, have examined originals or copies of such documents, corporate records, certificates of public officials and other instruments as we have deemed necessary or advisable for the purpose of rendering this opinion.

In rendering the opinion expressed herein, we have, without independent inquiry or investigation, assumed that (i) all documents submitted to us as originals are authentic and complete, (ii) all documents submitted to us as copies conform to authentic, complete originals, (iii) all signatures on all documents that we reviewed are genuine, (iv) all natural persons executing documents had and have the legal capacity to do so, (v) all statements in certificates of public officials and officers of the Company that we reviewed were and are accurate and (vi) all representations made by the Company as to matters of fact in the documents that we reviewed were and are accurate.

Based upon the foregoing, we advise you that, in our opinion, when the Securities have been issued and delivered against payment therefor in accordance with the terms of the Underwriting Agreement, the Securities will be validly issued, fully paid and non-assessable.

We are members of the Bars of the States of New York and California and the foregoing opinion is limited to the General Corporation Law of the State of Delaware.

We hereby consent to the filing of this opinion as an exhibit to a report on Form 8-K to be filed by the Company on the date hereof and its incorporation by reference into the Registration Statement and further consent to the reference to our name under the caption “Legal Matters” in the prospectus supplement, which is a part of the Registration Statement. In giving this consent, we do not admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act.

Very truly yours,

/s/ Davis Polk & Wardwell LLP