<PAGE>
                                                                 Exhibit 10.23

                    FIFTH AMENDMENT TO LIGHT INDUSTRIAL LEASE

         This Fifth Amendment to Light Industrial Lease (the "Fifth
Amendment"), dated as of March 23rd, 2000, is entered into by and between
TIAA Realty, Inc., a Delaware corporation "Lessor") and Gasonics
International, Inc., a California corporation ("Lessee").

                                    RECITALS

A.       Lessor's predecessor-in-interest, Teachers Insurance and Annuity
Association of America, a New York corporation, and Lessee's
predecessor-in-interest, Gasonics, Inc., entered into that certain Light
Industrial Lease dated October 25, 1989, as amended by that certain First
Amendment to Light Industrial Lease dated February 21, 1992, that certain
Second Amendment to Light Industrial Lease dated April 1, 1992, that certain
Third Amendment to Light Industrial Lease (undated) and that certain Fourth
Amendment to Light Industrial Lease dated July, 1999 (collectively, the
"Lease"), pursuant to which Lessor leased to Lessee the premises located at
2730-2760 Junction Avenue, San Jose, California, consisting of approximately
ninety thousand four hundred sixty-seven (90,467) square feet (the "Original
Premises").

B.       The Lease is scheduled to expire on December 31, 2001.

C.       Lessor and Lessee desire to (1) extend the term of the Lease with
respect to the Original Premises, (2) provide for Lessee's occupancy of
additional space consisting of a portion of the building located at 404-410
East Plumeria Drive, San Jose, California as of May 1, 2000 and (3) provide
for Lessee's occupancy of the remaining space in the building located at
404-410 East Plumeria Drive, San Jose, California as of approximately July 1,
2002, as more specifically provided in this Fifth Amendment.

         Now, therefore, for valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, Lessor and Lessee agree as
follow:

         1.    ADDITIONAL LEASED PREMISES: Lessor hereby leases to Lessee,
and Lessee leases from Lessor, the following:

               a.       404 EAST PLUMERIA. The premises consisting of
                        approximately twenty- seven thousand nine hundred
                        eight (27,908) rentable square feet of space in the
                        Montague Business Park, commonly known as 404 East
                        Plumeria Drive, San Jose, California (the "404 E.
                        Plumeria Premises").

               b.       410 EAST PLUMERIA. The premises consisting of
                        approximately twenty seven thousand five hundred
                        seventy-six (27,576) rentable square feet of space in
                        the Montague Business Park, commonly known as 410
                        East Plumeria Drive, San Jose, California (the "410
                        E. Plumeria Premises").

               The 404 E. Plumeria Premises and the 410 E. Plumeria Premises
and the real property of which they are a part are referred to hereinafter
collectively as the "Plumeria Property". All references in the Lease to the
"Premises" shall be deemed to refer to the Original Premises, and as of the
404 E. Plumeria Commencement Date and the 410 E. Plumeria


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Commencement Date, respectively, the 404 E. Plumeria Premises and the 410 E.
Plumeria Premises. Lessor and Lessee agree that the rentable square footage
of the Premises as set forth above shall be conclusive as between the parties
for the purposes of this Lease and that if a remeasurement of the Premises,
or any portion thereof, reflects a greater or lesser size, there shall be no
adjustment of the base Monthly Rent or any other amount payable finder the
Lease, as amended by this Fifth Amendment,

         2.    TERM.

               a.       COMMENCEMENT.

                        (1) The Term of the Lease for the Original Premises
                            has already commenced;

                        (2) The Term of the Lease for the 404 E. Plumeria
                            Premises shall commence on May 1, 2000 (the "404
                            E. Plumeria Commencement Date"); and

                        (3) The Term of the Lease for the 410 E. Plumeria
                            Premises shall commence on July 1, 2002 (the "410
                            E. Plumeria Commencement Date").

                        Provided, however, that if Lessor is unable to
                        deliver possession of the 404 E. Plumeria Premises
                        and/or the 410 E. Plumeria Premises by the dates
                        provided above, such failure shall not affect the
                        validity of this Lease nor shall it extend the Term
                        or render Lessor liable to Lessee for any loss or
                        damage resulting therefrom or delay the 404 E.
                        Plumeria Commencement Date except as provided in
                        Paragraph 9 of this Fifth Amendment. Notwithstanding
                        any other provision of this Lease, if Lessor cannot
                        deliver possession of the 410 E. Plumeria Premises to
                        Lessee for any reason including the fault of Lessor,
                        the Term of the Lease with respect to the 410 E.
                        Plumeria Premises shall instead commence on the date
                        on which Lessor tenders possession of the 410 E.
                        Plumeria Premises to Lessee.

               b.       EARLY OCCUPANCY. After execution of this Fifth
                        Amendment and the delivery by Lessee of the security
                        deposit, insurance certificates showing coverage for
                        the 404 E. Plumeria Premises in the amounts required
                        under the Lease and any other sums hereunder required
                        to be paid upon execution of this Fifth Amendment,
                        and upon Lessor obtaining possession of the 404 E.
                        Plumeria Premises, Lessee shall be provided with
                        access to the 404 E. Plumeria Premises for the
                        purpose of performing any alterations or improvements
                        and otherwise preparing for the occupancy of the 404
                        E. Plumeria PREMISES, provided, however, that any
                        alterations or improvements shall be undertaken in
                        compliance with the terms of the Lease. Such early
                        occupancy shall be on the terms and conditions
                        contained in the Lease, as amended by this Fifth
                        Amendment, provided,


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<PAGE>

                        however, that Lessee shall not be obligated to pay
                        base Monthly Rent prior to May 1, 2000.

               c.       TERMINATION. Paragraph 1.2 of the Lease is amended to
                        extend the Term through and including December 31,
                        2006. The Term of the Lease shall expire concurrently
                        for the Original Premises, the 404 E. Plumeria
                        Premises and the 410 E. Plumeria Premises.

         3.    MONTHLY RENT.

               a.       ORIGINAL PREMISES. Through December 31, 2001, the
                        Monthly Rent payable for the Original Premises shall
                        remain as specified in the Lease. Effective January
                        1, 2002 base Monthly Rent for the Original Premises
                        shall be as follows:

<TABLE>
<CAPTION>
                        Period                 Monthly Rent/RSF        Monthly Rent
                        ------                 ----------------        ------------
<S>                                                 <C>              <C>
                        1/1/02 - 4/30/02              $2.00            $180,934.00
                        5/1/02 - 4/30/03              $2.09            $189,076.03
                        5/1/03 - 4/30/04              $2.20            $199,027.40
                        5/1/04 - 4/30/05              $2.31            $208,978.77
                        5/1/05 - 4/30/06              $2.42            $218,930.14
                        5/1/06 - 12/31/06             $2.55            $230,690.85
</TABLE>

               b.       404 E. PLUMERIA. Lessee shall pay to Lessor base
                        Monthly Rent for the 404 E. Plumeria Premises as
                        follows:

<TABLE>
<CAPTION>
                        Period                 Monthly Rent/RSF        Monthly Rent
                        ------                 ----------------        ------------
<S>                                                 <C>              <C>
                        5/1/00 - 4/30/01              $1.90            $53,025.20
                        5/1/01 - 4/30/02              $2.00            $55,816.00
                        5/1/02 - 4/30/03              $2.09            $58,327.72
                        5/1/03 - 4/30/04              $2.20            $61,397.60
                        5/1/04 - 4/30/05              $2.31            $64,467.48
                        5/1/05 - 4/30/06              $2.42            $67,537.36
                        5/1/06 - 12/31/06             $2.55            $71,165.40
</TABLE>

               c.       410 E. PLUMERIA. Lessee shall pay to Lessor base
                        Monthly Rent for the 410 E. Plumeria Premises as
                        follows:

<TABLE>
<CAPTION>
                        Period                 Monthly Rent/RSF        Monthly Rent
                        ------                 ----------------        ------------
<S>                                                 <C>              <C>
                        7/1/02 - 4/30/03              $2.09            $57,633.84
                        5/1/03 - 4/30/04              $2.20            $60,667.20
                        5/1/04 - 4/30/05              $2.31            $63,700.56
                        5/1/05 - 4/30/06              $2.42            $66,733.92
                        5/1/06 - 12/31/06             $2.55            $70,318.80
</TABLE>


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         4.    TRIPLE-NET LEASE. Lessee acknowledges that the provisions of
Paragraph 4.3 of the Lease apply to the entire premises and that Lessee shall
pay all expenses of every kind as described in the Lease with respect to the
Original Premises, the 404 E. Plumeria Premises and the 410 E. Plumeria
Premises. Effective as of the 404 E. Plumeria Commencement Date, Lessee shall
pay fifty and three tenths percent (50.3%) of any expenses of the categories
described in the Lease insofar as Lessor incurs those expenses in connection
with the Plumeria Property. Effective as of the 410 E. Plumeria Commencement
Date, Lessee shall pay one hundred percent (100%) of any expenses of the
categories described in the Lease insofar as Lessor incurs those expenses in
connection with the Plumeria Property.

         5.    SECURITY DEPOSIT.

               a.       404 E. PLUMERIA. Upon execution of this Fifth
                        Amendment, Lessee shall increase the security deposit
                        required pursuant to Paragraph 4.5 of the Lease by
                        seventy-one thousand one hundred sixty-five and
                        40/100 dollars ($71,165.40). Upon execution of this
                        First Amendment, Lessee shall replace the existing
                        letter of credit with a new letter of credit in the
                        amount of one hundred forty thousand three hundred
                        fifty-eight and 40/100 dollars ($140,358.40) which
                        satisfies the requirements of Paragraph 22 of the
                        Lease.

               b.       410 E. PLUMERIA. On the day preceding the 410 E.
                        Plumeria Commencement Date, Lessee shall increase the
                        security deposit required pursuant to Paragraph 4.5
                        of the Lease by seventy thousand three hundred
                        eighteen and 80/100 dollars ($70,318.80). On the day
                        preceding the 410 E. Plumeria Commencement Date,
                        Lessee shall replace the existing letter of credit
                        with a new letter of credit in the amount of two
                        hundred ten thousand six hundred seventy-seven and
                        20/100 dollars ($210,677.20) which satisfies the
                        requirements of Paragraph 22 of the Lease.

         6.    CONDITION OF THE PREMISES. Lessee acknowledges and agrees that
Lessor shall have no obligation to perform or construct any other
alterations, improvements or additions to, or redecoration of, the Original
Premises, the 404 E. Plumeria Premises or the 410 E. Plumeria Premises except
as specifically provided in this Paragraph 6, and that Lessee shall accept
the Original Promises in their existing condition, and the 404 E. Plumeria
Premises and the 410 E. Plumeria Premises in the condition existing as of the
404 E. Plumeria Commencement Date and the 410 E. Plumeria Commencement Date,
respectively. Notwithstanding the foregoing (1) on May 1, 2000, the roof of
the Original Premises and the HVAC systems therein (excluding those serving
any clean room areas in the Original Premises) shall be brought into good
working condition and repair, (2) on the 404 E. Plumeria Commencement Date,
the roof of the 404 E. Plumeria Premises and the HVAC systems therein shall
be brought into good working condition and repair, and (3) on the 410 E.
Plumeria Commencement Date, the roof of the 410 E. Plumeria Premises and the
HVAC systems therein shall be brought into good working condition and repair.


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         7.    CONDEMNATION AND DAMAGE AND DESTRUCTION. The provisions of
Paragraphs 12 and 16 of the Lease shall apply separately to each of the
Original Premises, the 404 E. Plumeria Premises and the 410 E. Plumeria
Premises, it being the intent of the parties that if any of such distinct
positions of the Premises are condemned or damaged independently of the other
portions of the Premises, the Lease shall remain in effect for any portion of
the Premises if the terms of the Lease would not provide either party with
the right to terminate the Lease with respect to that portion of the Premises.

         8.    CROSS DEFAULT. Lessor and Lessee acknowledge and agree that
the payment and performance obligations contained in the Lease, as amended by
this Fifth Amendment, are not distinct obligations as far as they relate to
the Original Premises, the 404 E. Plumeria Premises and the 410 E. Plumeria
Premises, and that any default which would entitle Lessor to terminate the
Lease shall entitle Landlord to terminate the entire Lease, as amended by
this Fifth Amendment, and Lessee's right to occupy all portions of the
Premises.

         9.    RELEVANCE OF LIABILITY. Lessor has disclosed to Lessee that a
party previously negotiated with Lessor for the occupancy of the 404 E.
Plumeria Premises, Lessee hereby releases Lessor from all liability for any
costs, expenses or damages of any kind which Lessee may incur if such party
files a lawsuit with respect to the 404 E. Plumeria Premises, including,
without limitation, any costs incurred by Lessee in improving the 404 E.
Plumeria Premises, any damages resulting from delay or inability to deliver
possession of the 404 E. Plumeria Premises, and attorneys' fees and court
costs incurred by Lessee in connection therewith. If Lessor is prevented from
delivering possession of the 404 E. Plumeria Premises to Lessee as a result
of any such action for a period in excess of ninety (90) days, whether by
court order or otherwise, Lessee shall have the right, exercisable by
providing written notice within ten (10) days after the expiration of inch
ninety (90) day period, to terminate the Lease with respect to both (but not
one or the other of) the 404 E. Plumeria Premises and the 410 E. Plumeria
Premises and to terminate the Fifth Amendment in its entirety (in which case
Lessee shall continue to occupy the Original Premises pursuant to the terms
of the Lease [including the Term thereof]). If Lessee terminates the Lease
with respect to the 404 E. Plumeria Premises and the 410 E. Plumeria Premises
as provided in the preceding sentence but does not terminate this Fifth
Amendment in its entirety, all references to the 404 E. Plumeria Premises and
the 410 E. Plumeria Premises shall be deleted If Lessee fails to deliver such
notice, the Lease will remain in effect as to the entire Premises, provided
that Lessee shall not be obligated to pay any sums due for the 404 E.
Plumeria Premises unless and until possession is delivered.

         10.   SEPARATE LEASES. At any time during the Term of this Lease,
Lessor may require that Lessee enter into distinct leases on identical terms
and conditions as are contained in the Lease, as amended by this Fifth
Amendment (except for such terms as would become unnecessary as a result of
the separation of the lease of the Premises into distinct leases), pursuant
to which the Original Promises, the 404 E. Plumeria Premises and/or the 410
E. Plumeria Premises each would be the subject of a separate and distinct
lease (except that the 404 E. Plumeria Premises and the 410 E. Plumeria
Premises may be combined into one lease).

         11. In the event of a conflict between the terms and conditions of
the Lease and the terms and conditions of this Fifth Amendment, the terms and
conditions of this Fifth Amendment


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<PAGE>

shall control. Except as amended by this Fifth Amendment, the Lease is in
full force and effect and is hereby ratified by Lessor and Lessee.

         In witness whereof, Lessor and Lessee have entered into this Fifth
Amendment as of the date first hereinabove written.

Lessor                                   Lessee
------                                   ------

TIAA Realty, Inc., a Delaware            Gasonics International, Inc.,
                                         a California corporation

By:                                      By:  /s/ R. Rasmussen
   -------------------------------           ------------------------------
Name:                                    Name:  R. Rasmussen
     -----------------------------             ----------------------------
Title:                                   Title: CFO
       ---------------------------              ---------------------------


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