Exhibit 5


                              THELEN REID & PRIEST LLP
                                 ATTORNEYS AT LAW
                             TWO EMBARCADERO CENTER
                          SAN FRANCISCO, CA  94111-3995



                                  May 25, 1999



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


Ladies and Gentlemen:

     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
1,000,000 shares of common stock, $0.001 par value, of the Company ("Common
Stock"), pursuant to the Company's 1995 Stock Option Plan, as amended (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.

     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