A transistor, made of a solid piece of semiconductor material, is a semiconductor device used to amplify and switch electronic signals. It has at least three terminals for connection to an external circuit. A voltage or current applied to one pair of transistor’s terminals changes the current flowing through another pair of terminals. The transistor amplifies the signal since the controlled power can be much more than the controlling power. The transistor is a fundamental building block of modern electronic devices. The transistor paved the way for smaller and cheaper radios, calculators, and computers after its release in the 1950s.

Julius Edgar Lilienfeld filed the first patent, describing a device similar to a Field Effect Transistor, for a transistor in 1925. Lilienfeld published no research articles nor did the patent cite any examples of constructed devices. Oskar Heil patented a similar device in 1934. Herbert Mataré built a duodiodes that had two separate but close metal contacts on a semiconductor substrate and discovered effects that could not be explained by two independently operating diodes and thus discovered the basic idea for the later point contact transistor.

John Bardeen and Walter Brattain observed that when electrical contacts were applied to a crystal of germanium the output power was larger than the input. William Shockley saw the potential of this and worked to greatly expand the knowledge of semiconductors. John R. Pierce coined the term transistor. According to legal papers from the Bell Labs patent William Shockley and Gerald Pearson had built operational versions from Lilienfeld’s patents but never referenced this work in any of their research papers.

Texas Instruments produced the first silicon transistor in 1954. The transistor is a key component in almost all modern electronics and is considered one of the greatest inventions of the twentieth century. It is mass produced using a highly automated process that achieves astonishingly low per-transistor costs.

Most transistors are produced in integrated circuits, along with diodes, resistors, capacitors and other electronic components although there are several companies that produce over a billion individually packaged transistors every year.

Logic gates consist of up to about twenty transistors while a microprocessor can use as many as 2.3 billion transistors.
Transistor’s low cost, flexibility, and reliability have allowed for transistors to be used along with a computer program to carry out a control function rather than design an equivalent mechanical control function.

Bipolar junction transistor, BJT, is the most commonly used transistor in the 1960s and 70s. It still remains as the transistor of choice for many analog circuits such as simple amplifiers. MOSFETs captured nearly all market shares for digital circuits and more recently have taken over the analog and power applications as well which include modern clocked analog circuits, voltage regulators, amplifiers, and power transmitters.

Through gain, using a small signal applied to one pair of terminals to control a much larger signal on another pair of terminals, a transistor gains its usefulness. It can act as an amplifier or as an electric control switch capable of turning current on or off. The bipolar transistor has terminals labeled base, collector, and emitter where a small current at the base terminal controls a much larger current between the collector and emitter terminals. The field-effect transistor has terminals labeled gate, source, and drain which have a voltage at the gate that can control a current between source and drain.