silicon Valley 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. 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