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Exhibit 4.19.1
 
 Fourth Amendment to
Joint Venture Agreement dated 13 November 2002
  rd
  D-81669
      1. Section 1.4 including the changes made to it in the Third Amendment shall be replaced by the
following:
 1.4
    
    Limitations on Sale, Transfer and Other Disposition, and Use of Shares as Security
 1.4.1
    
    Within five (5) years after the incorporation of the Company, or until the shares of the
Company are listed on Taiwan Stock Exchange, or any stock exchange out of the Republic of China
(the Stock Exchange), whichever is earlier, neither Party shall, without the prior written
consent of the other Party, sell, transfer or otherwise dispose of its shares (except for, (i)
transfers of
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shares to an Affiliate, or (ii) transfers of shares to employees under Subsection 1.3-6, each under
the terms of this Agreement and in accordance with the provisions of the Articles of
Incorporation), or pledge, hypothecate or otherwise use its shares as security, or grant options
over its legal and beneficial interest in its shares. Any action of a Party violating this
provision shall be void and shall be considered a material breach of this Agreement in accordance
with Subsection 7.3 (a).
 1.4-2
    
    a) To the extent that the restrictions of Subsection 1.4.1 cease to apply (but subject to the
Minimum Shareholding under Subsection 1.4-4) and in the case that either Party desires to sell to a
bona fide third party all or any of its shares of the Company (such Party hereinafter the Selling
Party), the other Party shall have a right of first refusal to purchase such shares (except for
transfers of shares to an Affiliate under the terms of this Agreement and in accordance with the
provisions of the Articles of Incorporation). The Selling Party shall first give a written notice
to the other Party (hereinafter the Receiving Party) setting forth i) the number of shares
proposed to be transferred (hereinafter the Offered Shares), ii) the proposed purchase price,
terms and payment and other material terms and conditions received from a bona fide third party and
iii) an irrevocable offer to sell Offered Shares to the Receiving Party (hereinafter the Sale
Offer) at the same price
and on the same terms and conditions as set forth therein. For the avoidance of doubt, the right of
first refusal stipulated in this Subsection 1.4-2 shall apply only when i) the shares of the
Company remain unlisted after five (5) years of incorporation of the Company; or ii) in the case
where the shares of the Company are listed on the Stock Exchange, the right of first refusal
stipulated herein shall only apply for the Off-the-Market Sale of shares of the Company by either
Party.For the purpose of this Subsection 1.4-2, Off-the-Market Sale shall mean the sale of shares of the
Company not through the Stock Exchange or not via Depository Receipts.b) The Receiving Party shall have the right to purchase the Offered Shares pursuant to the Sale
Offer, in whole or in part, by delivering a written notice to the Selling Party within 30 days from
the date of the Sale Offer, irrevocably stating therein that all of the Offered Shares will be
purchased by the Receiving Party.c) If the Receiving Party provides to the Selling Party the notice specified in the immediately
preceding paragraph, then the Receiving Party shall have 30 days to complete the purchase of the
Offered Shares upon the terms set forth in the Sale Offer (hereinafter the Purchase Period),
provided, however, that the Purchase Period shall be extended until such date as all required
approvals, consents or authorizations in connection with such purchase are obtained.d) If the Receiving Party shall not have completed such purchase within the Purchase Period, as
extended as provided herein, then the Selling Party shall have the right for 90 days thereafter
(hereinafter the Transfer Period) to
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transfer the Offered Shares not subject to any of the restrictions set forth in this
Agreement; provided, however, that such transfer is consummated on terms not more favorable to the
purchasers thereof than the terms specified on the Sale Offer; and provided, further, that the
Transfer Period shall be extended until such date as all required approvals, consents or
authorizations in connection with such purchase are obtained.e) If at the end of the Transfer Period, as extended as provided herein, the Selling Party has not
completed the sale of the Offered Shares, the Selling Party shall no longer be permitted to sell
such Offered Shares pursuant to this Section 1.4.f) In case that any Party transfers all or part of its shares in the Company to a third party in
accordance with this Section 1.4-2, this Agreement shall not terminate and such Selling Party shall
remain liable to all obligations under this Agreement, and it is a precondition for such transfer
of shares that the Selling Party shall have caused such third party to enter into an undertaking to
the benefit of the other Party by which such third party agrees to be bound by the covenants of
this Agreement and to perform the obligations of the Selling Party under this Agreement.g) Notwithstanding anything to the contrary of other provisions set forth in this Section 1.4-2,
neither Party shall sell any of its shares of the Company to any Competitors of the Company via
either a Depository Receipt or an Off-the-Market Sale, or via after hour trading on the Stock
Exchange. For purposes of this Agreement, a Competitor shall mean a company which conducts
the businesses of development, manufacture or sale of semiconductor products
which are in competition with the Companys products at any time.1.4-3
    
    a) In case that a Party (Transferring Party) transfers all or part of its shares in the
Company to an Affiliate, this Agreement shall terminate with regard to the Transferring Party and
it is a precondition for such transfer of shares that the Transferring Party shall have caused such
Affiliate to enter into an agreement with the other Party, and the other Party agrees to enter into
such an agreement with the Affiliate, by which such Affiliate agrees to be bound by the covenants
of this Agreement and the Ancillary Agreements and to perform the obligations of the transferring
Party under this Agreement and the Ancillary Agreements.b) If the transfer of shares in the Company from the Transferring Party to an Affiliate occurs in
accordance with Section 1.4-3 (a) above, the Transferring Party undertakes and agrees, and shall
cause such Affiliate to undertake and agree, that should it at anytime cease to be an Affiliate of
the Transferring Party, such Affiliate will, duly transfer all its shares in the Company to the
Transferring Party or another Affiliate of the Transferring Party without undue delay (the
undertaking and agreement set forth above is referred to as the Re-transfer Obligation).
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c) The Parties acknowledge that the Company has recently submitted an IPO application to
Taiwan Stock Exchange and that the applicable laws and regulations require the Parties to put their
shares in the Company in lock-up (the Statutory Lock-up). In case that a Party decides to
transfer its shares in the Company to an Affiliate while some or all of its shares in the Company
are still subject to the Statutory Lock-up, the Transferring Party will use its best effort to seek
approval from the relevant governmental authorities for such transfer. The other Party agrees to
support the Transferring Party to obtain said governmental approvals.d) In case that, (i) the Transferring Party has transferred shares in the Company to an
Affiliate while the shares are still in Statutory Lock-up and (ii) while the shares are still in
Statutory Lock-up, the conditions for the Re-transfer Obligation as set forth in Section 1.4-3 (b)
are fulfilled, then the Transferring Party will use its best effort to seek approval from the
relevant governmental authorities for the transfer, as required under the Re-Transfer Obligation,
and the other Party agrees to support the Transferring Party to obtain said governmental approvals.
In case where the above approval cannot be obtained within 2 months from the date of filing of such
application for approval, the Transferring Party shall cause its Affiliate to, fulfill any part of
the Re-Transfer Obligation when applicable laws and regulations permit.e) In case that IFX will spin-off its memory products division to an Affiliate (the
MP-Affiliate) and transfer its shares in the Company to the MP-Affiliate as part of this
spin-off, the Re-transfer Obligation shall expire (i) [**] or (ii) five years after the effective
date of the spin-off, whichever is earlier.f) In case that, (i) the MP-Affiliate ceases to be an Affiliate of IFX, and (ii) [**], and (iii)
the failure to achieve the conditions of the preceding sub-paragraph (ii) is not attributable to
NTC or an event of Force Majeure, [**]1.4-4
    
    Minimum Shareholding
 (a) Notwithstanding anything to the contrary of other provisions set forth in this Article 1, each
Party together with its Affiliates shall own a minimum of 33.5% of the outstanding shares of the
Company at any time (the Minimum Shareholding) and shall not pledge, hypothecate or otherwise use
its shares as security, or grant options over its legal and beneficial interest in these 33.5% of
the outstanding shares (Encumbrance), with the understanding that if a Party transfers its shares
in the Company to an Affiliate as contemplated by Subsection 1.4-3 above, the Transferring Party
shall be relieved from the Minimum Shareholding obligation and the Affiliate shall forthwith
adhere to the Minimum Shareholding obligation.(b) Any action in violation of this provision shall be considered a material breach of this
Agreement according to Subsection 7.3 (a).
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(c) In case the non-breaching Party decides not to terminate this Agreement for material
breach according to Subsection 7.3(a), it may choose that each Partys Output Share shall be
adjusted by the following formula: The breaching Party shall be obligated to offer to the
non-breaching Party, and the non-breaching Party shall have the right of first refusal to the offer
from the breaching Party, a share of the Total Capacity amounting to 1.5[x]% of the Total Capacity
of the Company if the breaching Partys shareholding is [x]% less than 33.5% of the shares of the
Company, or if the breaching Partys shareholding free of any Encumbrance is [x]% less than 33.5%
of the shares of the Company. By way of example: If the breaching Partys shareholding is decreased
to 16% of the outstanding shares of the Company, it shall offer to the non-breaching Party 26.25%
(1.5[33.5-16])% of the Total Capacity. The terms Output Share and Total Capacity used in this
Subsection 1.4-4 shall have the same meaning as defined in the PPCRA and the Parties shall cause
the Company to comply with this Subsection 1.4-4.(d) Further to the rights of the non-breaching Party to terminate this Agreement pursuant to
Section 7.3 (a), or to claim an adjustment of the Output Share pursuant to Subsection 1.4-4 (c),
the breaching Party shall on written request of the non-breaching Party:
 -
    
    withdraw one of its appointed directors if the shareholding of the breaching Party drops below
30%;-
    
    withdraw two of its appointed directors if the shareholding of the breaching Party drops below 26%;-
    
    withdraw three of its appointed directors and its appointed supervisor if the
shareholding of the breaching Party drops below 22%;-
    
    withdraw four of its appointed directors and its appointed supervisor if the
shareholding of the breaching Party drops below 16.75%.
 1.4-5
    
    Depository Receipts Offering
 Subject to the Minimum Shareholding each Party shall be entitled to dispose of its shareholding in
the Company via the offering of depository receipts. If a Party intends to do so, it shall first
inform the other Party of the volume of shares to be offered and the anticipated price. The other
Party may request within 15 days to participate in such offering, or to buy the first Partys
shares intended to be offered via depository receipts, provided that the Parties can agree on the
conditions for such joint offering, or a price for the shares within the 15 days period. In any
event and even if there is no agreement within the above 15 days period, the Parties agree to cause
their nominees on the board of the Company to support such offerings and to vote affirmatively on
any resolution required for such offering. The Parties shall cause the Company to sponsor such
offering of depository receipts and to file all necessary applications, in particular with the
Securities and Futures Bureau.
 2. The following shall replace Subsection 2.3-1 (t):
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3. The following shall be added to the end of Section 7.5:
    4. The following shall be added to Subsection 8.4-1.4:
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5. The following shall be added to Section 8.5:
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Nanya Technology Corporation
    
    Infineon Technologies AGBy:          /s/ Jih Lien
    
    By:     /s/
Michael MajerusName: Jih Lien
    
    Name: Dr. Michael MajerusTitle: President
    
    Title: Group Vice-PresidentDate: March 22, 2006
    
    Date: March 22, 2006By:     /s/ Rudolf von MoreauName: Rudolf von MoreauTitle: Senior DirectorDate: March 22, 2006
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