**EXHIBIT
      10.55.1**





**CHANGE
      IN TERMS AGREEMENT**





This
      Change in Terms Agreement (this “CIT”) is made as of and delivered on April 17,
      2008, by and between Mission West Properties, Inc., a Maryland corporation
      (“Borrower”), and Heritage Bank of Commerce (the “Bank”).





**Recitals**





A.  As
      of
      March 4, 2008, the Bank and Borrower entered into certain agreements (the “March
      2008 Loan Documents”) including but not limited to a Revolving Credit Loan
      Agreement (the “Agreement”) pursuant to which the Bank agreed, subject to the
      terms and conditions set forth therein, to lend up to the sum of Ten Million
      Dollars ($10,000,000.00) to Borrower, and pursuant to which Borrower agreed
      to
      repay the loan on or before June 15, 2009.




B.  The
      Borrower now desires to borrow up to Seventeen Million Five Hundred Thousand
      Dollars and no cents ($17,500,000.00) from the Bank from time to time to meet
      the working capital needs of the Borrower; and





C.  The
      Bank
      is willing to provide such financing subject to the terms and conditions set
      forth in this Agreement.




In
      consideration of the premises and the mutual promises herein contained, Borrower
      and the Bank agree as follows:





**Agreement**





1.  Incorporation
      of Recitals .
      Each of
      the foregoing Recitals is hereby incorporated herein by this reference as though
      set forth in full herein.





2.   Commitment
      Amount .
      The
      definition of “Commitment Amount” in Section
      1.1 of
      the
      Revolving Credit Loan Agreement is hereby replaced in full by the following:
      “Commitment Amount” shall mean, as of any applicable date of determination,
      Seventeen Million Five Hundred Thousand Dollars ($17,500,000.00)."





3.  Minimum
      Loan Fee .
      The
      first sentence in Section
      2.9.1 of the
      Agreement is hereby deleted and replaced by the following: “The Borrower shall
      pay to the Bank a minimum loan fee of Seventeen Thousand Five Hundred Dollars
      ($17,500.00) (the “Minimum Loan Fee”).”





4.  Conditions
      Precedent .
      At the
      Bank’s sole and absolute option and for its benefit, the effectiveness of this
      CIT and Bank’s obligations hereunder are conditioned upon the satisfaction of
      each and all of the following conditions on or before April 17,
      2008:





(a)  Borrower
      shall have paid to the Bank the sum of Seven Thousand Five Hundred Dollars
      ($7,500.00) in order to bring its currently paid Minimum Loan Fee of Ten
      Thousand Dollars to the required total of Seventeen Thousand Five Hundred
      Dollars ($17,500,000.00).





(b)  Borrower
      shall have paid one-half of Bank’s attorneys’ fees incurred in preparing this
      Agreement and any related documents in the current estimated sum of Nine Hundred
      Dollars ($900.00.), Borrower’s share Four Hundred Fifty Dollars
      ($450.00)





(c)  Borrower
      shall have executed and delivered to the Bank an Amended and Restated Revolving
      Credit Note (the “Amended Note”) in the form attached hereto as Exhibit
      A .
      All
      references in the Agreement to either the “Revolving Credit Note” or the “Note”
shall refer to the original Revolving Credit Note until such time as Borrower
      executes and delivers the Amended Note, after which time all references in
      the
      Revolving Credit Loan Agreement to either the “Revolving Credit Note” or the
“Note” shall refer to the Amended Note.





(d)  Borrower
      shall have provided to the Bank a copy of resolutions of the Board of Directors
      of the Borrower in form satisfactory to the Bank in its sole and absolute
      discretion authorizing the execution, delivery, and performance of this CIT,
      the
      borrowing hereunder, and the Amended Note, which shall have been certified
      by
      the Secretary or Assistant Secretary of the Borrower as of the date of delivery
      as being complete, accurate, and in effect by a certification in the form
      attached hereto as Exhibit
      B .





5.  No
      Other Changes to March 2008 Loan Documents .
      Except
      as expressly stated in this CIT or the Amended Note, there are no other changes
      or modifications to the March 2008 Loan Documents, and all terms of the March
      2008 Loan Documents remain in effect.





IN
      WITNESS WHEREOF, the Borrower and the Bank have caused this CIT to be executed
      by their duly authorized officers as of the day and year first written above.





MISSION
                WEST PROPERTIES, INC.A
                Maryland corporationBy:
            /s/
                Raymond V. MarinoPrint Name:
            Raymond
                V. MarinoIts:
            President
                & COOHERITAGE
                BANK OF COMMERCEBy:
            /s/
                Roxanne VaneIts:
            Senior
                Vice President





**AMENDED
      AND RESTATED REVOLVING CREDIT NOTE**


$17,500,000.00
              San
                  Jose, California





April
      17,
      2008





FOR
      VALUE
      RECEIVED, the undersigned promises to pay to the order of HERITAGE BANK OF
      COMMERCE (the “Bank”) at 150 Almaden Boulevard, San Jose, California (or such
      other place as Bank may designate), on June 15, 2009 (the “Termination Date”),
      the principal sum or so much of the principal sum of Seventeen Million Five
      Hundred Thousand Dollars ($17,500,000.00) as may from time to time have been
      advanced and be outstanding under that certain Revolving Credit Loan Agreement
      dated March 4, 2008, between the undersigned and the Bank (the “Agreement”) plus
      all accrued but unpaid interest thereon. Capitalized terms used herein without
      definition shall have the same meanings as in the Agreement.





The
      unpaid principal amount of this Note shall bear interest at the rate provided
      in
      the Agreement, which Agreement, as it may be amended from time to time, is
      by
      this reference incorporated herein and made a part hereof. Interest shall be
      payable to the extent accrued on the first day of each consecutive calendar
      month, beginning March 4, 2008, with all remaining interest due and payable
      on
      the Termination Date.





This
      Note
      is a Master Note under which sums must be repaid from time to time, and under
      which Revolving Loans may be made by the Bank up to the Commitment Amount,
      pursuant to the terms and conditions of the Agreement, and the books and records
      of the Bank shall constitute prima facie evidence of the amount of the
      Indebtedness at any time owing hereunder or under the Agreement, provided,
      however, that the failure by the Bank so to record any such amount or any error
      in so recording any such amount shall not limit or otherwise affect the
      obligations of the Borrower under this Note or the Agreement to repay the
      principal amount of all the Revolving Loans outstanding together with all
      interest accrued or accruing thereon.





The
      unpaid principal amount of all Revolving Loans, unless accelerated in accordance
      with the terms of the Agreement, if not paid sooner, will be due and payable,
      together with all accrued and unpaid interest and all other amounts due and
      unpaid under the Agreement, on the Termination Date.





Interest
      on the Revolving Loans is payable in arrears on the first day of each month
      during the term of the Agreement and as set forth in the Agreement. The
      Agreement provides for the payment by Borrower of various other charges and
      fees
      in addition to interest charges as more fully set forth in the
      Agreement.





All
      payments of any amount becoming due under this Note shall be made in the manner
      provided in Section
      2.11 of the
      Agreement.





Reference
      is made to the Agreement for, among other things, the conditions under which
      this Note may or must be paid in whole or in part prior to the Termination
      Date
      (whether accelerated or otherwise).





If
      an
      Event of Default (as defined in the Agreement) occurs and is not cured within
      the time provided for by the Agreement, the Bank may exercise any one or more
      of
      the rights and remedies granted by the Agreement or any of the Loan Documents
      or
      available under applicable law, including without limit the right to accelerate
      this Note or the Indebtedness, and may set off against the principal of and
      interest on this Note or against any other Indebtedness (i) any amount owing
      by
      the Bank to the undersigned, (ii) any property of the undersigned at any time
      in
      the possession of the Bank or any Affiliate (as that term is defined in the
      Agreement) of the Bank and (iii) any amount in any deposit or other account
      (including without limit an account evidenced by a certificate of deposit)
      of
      the undersigned with the Bank or any Affiliate of the Bank.





The
      undersigned and its successors and assigns and all accommodations parties,
      guarantors and endorsers (i) waive presentment, demand, protest and notice
      of
      dishonor, (ii) agree that no extension or indulgence to the undersigned or
      release or non-enforcement of any security, with or without notice, shall affect
      the obligations of any accommodation party, guarantor or endorser, and (iii)
      agree to reimburse the holder of this Note for any and all costs and expenses
      incurred in collecting or attempting to collect any and all principal and
      interest under this Note (including, but not limited to, court costs and
      attorney fees, whether in-house or outside counsel is used and whether such
      costs and expenses are incurred in formal or informal collection actions,
      federal bankruptcy proceedings, appellate proceedings, probate proceedings,
      or
      otherwise, all as more specifically set forth in Sections
      8.7 and 8.8 of the
      Agreement). This Note shall be governed by and construed in accordance with
      the
      laws of the State of California.





IN
      WITNESS WHEREOF, this Note has been delivered and accepted at Cupertino,
      California and the undersigned has executed this Note as of the 17th day of
      April, 2008.





MISSION
                WEST PROPERTIES, INC.A
                Maryland corporationBy:
            /s/
                Raymond V. MarinoPrint Name:
            Raymond
                V. MarinoIts:
            President
                & COO