Exhibit 5.1


November 8, 2000




Axcelis Technologies, Inc.
55 Cherry Hill Drive
Beverly, Massachusetts  01915


Ladies and Gentlemen:

         We are counsel to Axcelis  Technologies,  Inc. (the  "Company")  and we
have acted as counsel for the Company in connection  with the preparation of the
Registration  Statement  on  Form  S-8 to be  filed  by  the  Company  with  the
Securities and Exchange Commission for the registration under the Securities Act
of 1933,  as amended,  of 7,500,000  shares of the Company's  common stock,  par
value $0.001 per share (the "Shares"),  which are to be issued from time to time
to certain  employees of the Company and its  affiliates in connection  with the
Axcelis Technologies, Inc. Employee Stock Purchase Plan (the "Plan").

         We have examined the originals,  certified  copies or copies  otherwise
identified to our  satisfaction  as being true copies of the Plan and such other
documents  as we have  deemed  necessary  or  appropriate  for  purposes of this
opinion.

         Based on the foregoing, we are of the opinion that the Shares have been
duly and validly authorized and reserved for issuance, and that the Shares, when
issued under the terms of the Plan,  will be legally and validly  issued,  fully
paid and nonassessable.

         We hereby  consent to the filing of this  opinion as Exhibit 5.1 to the
Registration Statement.

                                              Very truly yours,

                                              /s/ Kirkpatrick & Lockhart LLP