| the area in northern California, southwest of San Francisco in the Santa Clara valley region, where many of the high-technology design and manufacturing companies in the semiconductor industry are concentrated. |
Sil·i·con Valley  (sĭl'ĭ-kən, -kŏn')  A region of western California southeast of San Francisco known for its high-technology design and manufacturing industries. |
A region on the San Francisco Peninsula in California where the miniaturized electronics industry is centered, so called because most of the devices built there are made of semiconductors such as silicon.
Note: The term is often used as a catchword to describe the development of high-tech industry: “If we can attract this corporation to our town, we could become another Silicon Valley.”
Silicon Valley
Nickname for the region in North California (around San Jose) that contains a huge concentration of computer and Internet companies.
Investopedia Commentary
In case you we're wondering, Silicon is the semiconductor material used to produce the computer chips that have made the Internet possible.
See also: Creative Destruction, Dot-Com, New Economy, Siliconaires