EXHIBIT 5



[Letterhead of Thelen Reid & Priest LLP]









                                  May 16, 2003



Advanced Energy Industries, Inc.
1625 Sharp Point Drive
Fort Collins, CO  80525

         Re:  REGISTRATION STATEMENT ON FORM S-8:  2003 STOCK OPTION PLAN

Dear Sirs:

         We have acted as counsel for Advanced Energy Industries, Inc., a
Delaware corporation (the "Company"), in connection with the preparation of the
Registration Statement on Form S-8 relating to the issuance and sale of
3,250,000 shares of common stock, $0.001 par value, of the Company ("Common
Stock"), pursuant to the Company's 2003 Stock Option Plan (the "Plan").

         Please be advised that we are of the opinion that the Common Stock to
be offered and sold by the Company, when issued and paid for in the manner
contemplated by the Plan, will be legally issued, fully paid and non-assessable.

         We are members of the bar of the State of California and we express no
opinion as to the laws of any state or jurisdiction other than federal laws of
the United States, the laws of the State of California and the corporate laws of
the State of Delaware (which includes applicable provisions of the Delaware
Constitution, the Delaware General Corporation Law and reported judicial
decisions interpreting these laws).

         We hereby consent to the filing of this opinion with the Securities and
Exchange Commission as an exhibit to the Registration Statement on Form S-8.


                                                   Very truly yours,



                                                   /s/ Thelen Reid & Priest LLP
                                                   THELEN REID & PRIEST LLP