A transistor is a sandwich of dissimilar semiconductors to which are attached three electrodes. …—© Merriam-Webster Inc.

Solid-state semiconductor device for amplifying, controlling, and generating electrical signals. Invented at Bell Labs (1947) by John Bardeen, Walter H. Brattain, and William B. Shockley, it displaced the vacuum tube in many applications. Transistors consist of layers of different semiconductors produced by addition of impurities (such as arsenic or boron) to silicon. These impurities affect the way electric current moves through the silicon. Transistors were pivotal in the advancement of electronics because of their small size, low power requirements, low heat generation, modest cost, reliability, and speed of operation. Single transistors were superseded in the 1960s and '70s by integrated circuits; present-day computer chips contain millions of transistors. Today transistors perform many different functions in nearly every type of electronic equipment.

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