Exhibit 5.1

BEIJING   BOSTON   BRUSSELS   DUBAI   FRANKFURT JOHANNESBURG   LONDON   LOS ANGELES   NEW YORK PALO ALTO   SAN FRANCISCO   SEOUL   SHANGHAI   WASHINGTON	Covington & Burling LLP One International Place Suite 1020 Boston, MA 02110-2600 T + 16176038800

May 29, 2025

Axcelis Technologies, Inc.

108 Cherry Hill Drive

Beverly, Massachusetts 01915

Ladies and Gentlemen:

We have acted as counsel to Axcelis Technologies, Inc., a Delaware corporation (the “Company”), in connection with the registration by the Company under the Securities Act of 1933, as amended (the “Act”), of 3,000,000 shares (the “Shares”) of the Company’s common stock, par value $0.001 per share (the “Common Stock”), issuable under the Axcelis Technologies, Inc. 2012 Equity Incentive Plan, as amended (the “Plan”), pursuant to the Registration Statement on Form S-8 filed with the Securities and Exchange Commission on the date hereof (such registration statement is referred to herein as the “Registration Statement”).

We have reviewed such corporate records, certificates and other documents, and such questions of law, as we have considered necessary or appropriate for the purposes of this opinion. We have assumed that all signatures are genuine, that all documents submitted to us as originals are authentic and that all copies of documents submitted to us conform to the originals.

We have relied as to certain matters on information obtained from public officials, officers of the Company and other sources believed by us to be responsible.

Based upon the foregoing, we are of the opinion that the Shares have been duly authorized and, when issued and paid for in accordance with the terms of the Plan, and any individual agreements relating to such Shares, the Shares will be validly issued, fully paid and non-assessable.

We are members of the bar of the Commonwealth of Massachusetts. We do not express any opinion herein on any laws other than the General Corporation Law of the State of Delaware and reported judicial decisions interpreting these laws.

We hereby consent to the filing of this opinion as Exhibit 5.1 to the Registration Statement. In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act.