As filed with the Securities and Exchange Commission on March 17, 2005

                                                      Registration No. 333-80369


                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549

                         POST EFFECTIVE AMENDMENT NO. 1
                                   TO FORM S-8

                        REGISTRATION STATEMENT UNDER THE
                             SECURITIES ACT OF 1933

                          Mission West Properties, Inc.
             (Exact name of registrant as specified in its charter)

           Maryland                                        95-2635431
(State or other jurisdiction of                (IRS employer identification no.)
 incorporation or organization)

                               10050 Bandley Drive
                               Cupertino, CA 95014
                                 (408) 725-0700
                    (Address of principal executive offices)

              Mission West Properties, Inc. 1997 Stock Option Plan
                            (Full title of the plan)

                                Mr. Carl E. Berg
                               10050 Bandley Drive
                               Cupertino, CA 95014
                                 (408) 725-0700
                     (Name and address of agent for service)

                                   Copies to:
                                  Alan B. Kalin
                              Bingham McCutchen LLP
                             1900 University Avenue
                          East Palo Alto, CA 94303-2223
                               Tel: (650) 849-4400
                               Fax: (650) 849-4800






                            DEREGISTRATION OF SHARES

On November 24, 2004, the  stockholders  of Mission West  Properties,  Inc. (the
"Registrant")  voted to approve for adoption the 2004 Equity Incentive Plan (the
"2004 Plan") to replace the 1997 Stock Option Plan  ("Predecessor  Plan").  This
Post-Effective  Amendment No. 1 to the Registrant's  Registration  Statement No.
333-80369 on Form S-8 filed on June 10, 1999 (the  "Registration  Statement") is
filed to deregister an aggregate of 3,991,089 shares previously  registered that
remain  available for issuance under the Predecessor  Plan. The 3,991,089 shares
deregistered  by this  Post-Effective  Amendment No. 1 will be registered,  by a
subsequently filed registration statement on Form S-8 for the 2004 Plan, and the
associated  registration  fee paid by the Registrant to register shares issuable
under the Predecessor Plan on the Registration Statement will be carried forward
and applied to the  registration fee necessary to register shares issuable under
the  Registrant's  2004 Plan. There remain 767,000 shares subject to outstanding
options  previously  granted under the  Predecessor  Plan, and the  Registration
Statement  will  remain  in  effect  to cover  the  potential  exercise  of such
outstanding options.






                                   SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, as amended, the
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-8 and has duly caused this Registration
Statement  to be  signed  on its  behalf  by  the  undersigned,  thereunto  duly
authorized,  in the City of Cupertino,  State of California,  on the 17th day of
March, 2005.

                                  Mission West Properties, Inc.


                                  By: /s/ Carl E. Berg                    
                                  ----------------------------------------------
                                  Carl E. Berg
                                  Chief Executive Officer

     Pursuant to the  requirements  of the  Securities  Act of 1933, as amended,
this  Post-Effective  Amendment  No. 1 to the  Registration  Statement  has been
signed by the following persons in the capacities indicated on March 17, 2005.



Signature                                 Title

/s/ Carl E. Berg                          Chairman of the Board, Chief Executive
--------------------------------------    Officer, and Director
Carl E. Berg

/s/ Raymond V. Marino                     President, Chief Operating Officer and
--------------------------------------    Director
Raymond V. Marino

/s/ Wayne N. Pham                         Vice President of Finance and 
--------------------------------------    Controller                  
Wayne N. Pham

/s/ John C. Bolger                        Director
--------------------------------------                      
John C. Bolger

/s/ William A. Hasler                     Director
--------------------------------------                  
William A. Hasler

/s/ Lawrence B. Helzel                    Director
--------------------------------------               
Lawrence B. Helzel