Exhibit 5.1

DLA Piper LLP (US)

4365 Executive Drive, Suite 1100

San Diego, California 92121-2133

O 858.677.1400

F 858.677.1401

W www.dlapiper.com

February 28, 2013

Securities and Exchange Commission

450 Fifth Street, N.W.

Washington, D.C. 20549

Ladies and Gentlemen:

As legal counsel for Cohu, Inc., a Delaware corporation (the “Company”), we are rendering this opinion in connection with the registration under the Securities Act of 1933, as amended, of up to 1,400,000 shares of the Common Stock, $1.00 par value (the “Registration Statement”), of the Company which may be issued pursuant to the exercise of options and other awards granted under the Cohu, Inc. 2005 Equity Incentive Plan (the “Plan”).

We have examined all instruments, documents and records which we deemed relevant and necessary for the basis of our opinion hereinafter expressed. In such examination, we have assumed the genuineness of all signatures and the authenticity of all documents submitted to us as originals and the conformity to the originals of all documents submitted to us as copies. We express no opinion concerning any law other than the law of the State of California, the corporation laws of the State of Delaware and the federal law of the United States. As to matters of Delaware corporation law, we have based our opinion solely upon our examination of such laws and the rules and regulations of the authorities administering such laws, all as reported in standard, unofficial compilations. We have not obtained opinions of counsel licensed to practice in jurisdictions other than the State of California.

Based on such examination, we are of the opinion that the 1,400,000 shares of Common Stock which may be issued under the Plan are duly authorized shares of the Company’s Common Stock, and, when issued against receipt of the consideration therefor in accordance with the provisions of the Plan, will be validly issued, fully paid and nonassessable.

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement and the use of our name wherever it appears in said Registration Statement. In giving this consent, we do not admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act, the rules and regulations of the Securities and Exchange Commission promulgated thereunder or Item 509 of Regulation S-K.

This opinion letter is given to you solely for use in connection with the issuance of the Shares in accordance with the Registration Statement and is not to be relied upon for any other purpose. Our opinion is expressly limited to the matters set forth above, and we render no opinion, whether by implication or otherwise, as to any other matters relating to the Company, the Shares or the Registration Statement.

Respectfully submitted,

/s/ DLA PIPER LLP (US)