<Tr> <Th> Summer (DST) </Th> <Td> PDT (UTC − 7) </Td> </Tr> <P> Silicon Valley is a nickname for the southern portion of the San Francisco Bay Area, in the northern part of the U.S. state of California . The "valley" in its name refers to the Santa Clara Valley in Santa Clara County, which includes the city of San Jose and surrounding cities and towns, where the region has been traditionally centered . The region has expanded to include the southern half of the San Francisco Peninsula in San Mateo County, and southern portions of the East Bay in Alameda County . </P> <P> The word "silicon" originally referred to the large number of silicon chip innovators and manufacturers in the region, but the area is now the home to many of the world's largest high - tech corporations, including the headquarters of 39 businesses in the Fortune 1000, and thousands of startup companies . Silicon Valley also accounts for one - third of all of the venture capital investment in the United States, which has helped it to become a leading hub and startup ecosystem for high - tech innovation and scientific development . It was in the Valley that the silicon - based integrated circuit, the microprocessor, and the microcomputer, among other key technologies, were developed . As of 2013, the region employed about a quarter of a million information technology workers . </P> <P> As more high - tech companies were established across the Santa Clara Valley, and then north towards the Bay Area's two other major cities, San Francisco and Oakland, the "Silicon Valley" has come to have two definitions: a geographic one, referring to Santa Clara County, and a metonymical one, referring to all high - tech businesses in the Bay Area or even in the United States . The term is now generally used as a synecdoche for the American high - technology economic sector . The name also became a global synonym for leading high - tech research and enterprises, and thus inspired similar named locations, as well as research parks and technology centers with a comparable structure all around the world . </P>

Which industry has a large presence in the silicon valley