HSINCHU, Taiwan, June 1, 2005 - UMC (NYSE: UMC TSE: 2303), a world leading semiconductor foundry, reached a major milestone with the celebration of its 25th anniversary this month. Since its establishment as Taiwan's first semiconductor company in 1980, UMC has grown to become a major global IC foundry service provider at the forefront of system-on-chip (SoC) production technology. The company's ability to thrive for a quarter of a century in one of the world's most competitive and challenging industries was highlighted in 2004 with record high revenues of US $3.7 Billion.

Robert Tsao, Chairman of UMC, said, "Over the last 25 years, UMC has established itself as a world leader in the semiconductor foundry industry. With our superior technical staff, state-of-the-art production facilities, and outstanding foundry service infrastructure, the company's potential can stretch as far as the vision of our employees. This is indeed a positive time for the company. In the coming years, I believe that UMC's employees and shareholders will continue to benefit from the years of effort that have led to this important anniversary."

UMC was initially founded as a small-scale IDM chip manufacturing company in 1980, that licensed technology from RCA to enable the delivery of its first product: an electronic watch IC. The company began its transformation into a pure play foundry in 1995 by establishing three separate joint-venture foundry companies. UMC acquired a fourth local foundry company in 1998, and in 2000 the group completed Taiwan's largest ever merger with the consolidation of the five joint-venture companies into a single foundry, UMC. Today, UMC is delivering world-leading technology such as 90nm and 65nm silicon and has customer products that cover all 3C (Computer, Consumer, and Communications) applications.

UMC has distinguished itself over its 25-year history with innovative and strategic business practices. It was the first company in Taiwan to introduce a stock bonus plan for its employees, a measure now widely adopted in every sector of Taiwan's technology industry. UMC was also the first semiconductor company to list on the Taiwan stock exchange, and in 2000, the company listed on the New York Stock Exchange. UMC was also the first foreign company to acquire a Japanese semiconductor company in 1997; UMCJ now operates as the only pure play foundry in Japan.

"UMC's 25th anniversary has come at an exciting time, as we are seeing widespread adoption of our 90nm process technology by customers throughout the electronics sector," stated UMC CEO, Dr. Jackson Hu. "We are looking forward to seeing this new generation of electronics products emerge into the mainstream within the next year. As we celebrate our silver anniversary, we remain strongly committed to providing the design, manufacturing, and technology resources our customers need to successfully bring their advanced SoC products to market."

Some of the statements in the foregoing announcement are forward looking within the meaning of the U.S. Federal Securities laws, including statements about future outsourcing, wafer capacity, technologies, business relationships and market conditions. Investors are cautioned that actual events and results could differ materially from these statements as a result of a variety of factors, including conditions in the overall semiconductor market and economy; acceptance and demand for products from UMC; and technological and development risks.

UMC (NYSE: UMC, TSE: 2303) is a leading global semiconductor foundry that manufactures advanced process ICs for applications spanning every major sector of the semiconductor industry. UMC delivers cutting-edge foundry technologies that enable sophisticated system-on-chip (SoC) designs, including 90nm copper, 0.13um copper, and mixed signal/RFCMOS. UMC is also a leader in 300mm manufacturing; Fab 12A in Taiwan and Singapore-based Fab 12i are both in volume production for a variety of customer products. UMC employs approximately 10,500 people worldwide and has offices in Taiwan, Japan, Singapore, Europe, and the United States. UMC can be found on the web at http://www.umc.com.