Transistor

Notes

Invented at Bell Labs in 1947; counting transistors per die remains the industry's headline measure of progress.

Overview

A transistor is a semiconductor device with three terminals in which a voltage or current on one terminal controls the current flowing between the other two, so it can act as a switch or an amplifier. It is the basic building block of all modern electronics: a single chip can contain billions of transistors, and almost all of them are MOSFETs, metal oxide semiconductor field effect transistors.

How it works

In a MOSFET, a gate sits over a channel region of silicon, separated from it by a very thin insulator. Voltage on the gate attracts or repels charge carriers in the channel, turning on or cutting off current between the source and the drain. An n-channel MOSFET conducts with electrons when its gate is high; a p-channel MOSFET conducts with holes when its gate is low. Pairing the two gives CMOS logic, which draws little current except when switching, the reason CMOS dominates digital chips.

Bipolar transistors work differently: a small current into the base controls a larger current between collector and emitter. They remain common in analogue, radio frequency and power circuits, and in BiCMOS processes that combine both types.

The transistor was invented at Bell Labs in 1947, when John Bardeen and Walter Brattain demonstrated the point-contact transistor, followed by William Shockley's junction transistor; the three shared the 1956 Nobel Prize in Physics. Mohamed Atalla and Dawon Kahng demonstrated the MOS transistor at Bell Labs in 1960. As MOSFETs shrank, their shape changed to keep control of the channel: planar devices gave way to FinFETs, with the channel standing up as a fin, and then to gate-all-around devices, in which the gate surrounds stacked sheets of silicon.

Examples

• The billions of FinFET or gate-all-around transistors in a modern processor.
• A CMOS inverter, the simplest logic gate, built from one n-channel and one p-channel transistor.
• A discrete power MOSFET switching current in a motor drive or power supply.
• A silicon germanium bipolar transistor in a radio frequency amplifier.
• A replica of the 1947 point-contact transistor in a museum collection.

Why it matters

Transistors are what device engineers, process integration engineers and TCAD specialists design and build, what circuit designers size and simulate, and what the design kit's models describe. Their speed, leakage, variability and reliability set the performance and power of every chip on a process.

In the chip lifecycle, the transistor is defined during technology and process development, characterised and modelled for the design kit, and monitored in production through test structures on every wafer.

It matters most to: Advanced Node Process Integration Engineer, Device Engineer, Device Physicist, Process Integration Engineer, TCAD Engineer

Common confusions

Not the same as transistor radio

A transistor radio is a portable radio from the era when transistors replaced valves. In the industry, transistor always means the device.

Not the same as gate

A logic gate, such as NAND, is a small circuit built from several transistors. The gate of a transistor is one of its terminals.

Not the same as chip

A chip contains many transistors and other devices. A discrete transistor is packaged on its own.

Sources

1. The Nobel Prize in Physics 1956 (opens in a new tab), Nobel Prize Outreach, 2026-10-22
2. 1947: Invention of the Point-Contact Transistor (The Silicon Engine) (opens in a new tab), Computer History Museum, 2026-10-22
3. 1960: Metal Oxide Semiconductor (MOS) Transistor Demonstrated (The Silicon Engine) (opens in a new tab), Computer History Museum, 2026-10-22
4. Transistor (Wikipedia) (opens in a new tab), Wikimedia Foundation, 2026-10-22
5. MOSFET (Wikipedia) (opens in a new tab), Wikimedia Foundation, 2026-10-22

Related terms

• Semiconductor
• PN junction
• n-type
• Moore's Law

Where it appears on the Hub

Used on 99 pages of the Hub. In each group, the pages that mention it most come first.