What is a transistor?

A transistor is a semiconductor device that amplifies, controls, and generates electrical signals and acts as the active components of integrated circuits. With three electrical leads, the emitter, collector, and base, a signal applied to the base influences the semiconductor material's ability to conduct electrical current between the emitter and collector. Invented in 1947 by John Bardeen, Walter H. Brattain, and William B. Shockley, the transistor replaced the electron tube by the late 1950s because of its small size, minimal heat generation, high reliability and low power consumption. The most common application of transistors today is for computer memory chips and microprocessors, where millions of components are embedded in a single integrated circuit.

What are the main parts of a transistor?

A transistor is a semiconductor device that amplifies, controls, and generates electrical signals. There are typically three electrical leads in a transistor. The three parts of a transistor are: * Emitter Emits or injects carriers into the base region. * Base The signal applied to the base influences the semiconductor material’s ability to conduct electrical current. * Collector Collects carriers injected from a nearby junction. In modern switching applications, the emitter, collector, and base are called the source, the drain, and the gate, respectively.

How does a transistor work in an electronic circuit?

A transistor is a semiconductor device that amplifies, controls, and generates electrical signals within circuits. It has three electrical leads: the emitter, collector, and base (or, in modern applications, the source, drain, and gate). A signal applied to the base (or gate) affects the material's ability to conduct current between the emitter (or source) and collector (or drain). Acting as a switch, voltage applied to the gate determines whether current flows from the source to the drain. Current flow means the circuit is "on", while no current flow means it is "off." These on/off states correspond to the binary 1s and 0s used in digital computers. Transistors can also act as amplifiers, where the input signal and the larger output signal are replicas of each other.

What are the different types of transistors?

Transistors amplify, control, and generate electrical signals in circuits. They have three leads: the emitter, collector, and base (or source, drain, and gate). Applying a signal to the base or gate affects the material's ability to conduct current between the emitter/source and collector/drain. Two main types of transistors are: * Bipolar transistors use both holes and electrons for conduction, with regions called the emitter, base, and collector. They're faster than FETs but use more current, suitable for high-speed applications like radio-frequency ICs. * Field-effect transistors (FETs) , including metal-oxide-semiconductor field-effect transistors (MOSFETs), have a source, drain, and gate. MOSFETs come in n-channel and p-channel types. There are also depletion-mode and enhancement-mode FETs.

How is a transistor used as a switch or an amplifier?

A transistor can act as either a switch or an amplifier in electronic circuits. Switch In digital circuits, transistors operate as switches. Applying a voltage to the gate controls current flow between the source and drain. The transistor is "on" when current flows and "off" when it doesn't, corresponding to binary 1s and 0s. Amplifier In amplifier circuits, transistors act as linear devices. A small signal applied to the base (or gate) controls a larger current between the emitter and collector (or source and drain), amplifying the input signal.

Why are transistors important for modern electronic devices?

Transistors are vital to modern electronic devices because they amplify, control, and generate electrical signals. They are the active components of integrated circuits or microchips, which may contain billions of these tiny devices. Transistors replaced vacuum tubes because they are smaller, generate less heat, are more reliable, and consume less power, enabling the miniaturization of complex circuits. They function as switches in computer memory chips and microprocessors, with their potential switching speeds reaching hundreds of gigahertz. In essence, transistors have become the nerve cells of the Information Age.

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NMOS transistorNegative-channel metal-oxide semiconductors (NMOS) employ a positive secondary voltage to switch a shallow layer of p-type semiconductor material below the gate into n-type. For positive-channel metal-oxide semiconductors (PMOS), all these polarities are reversed. NMOS transistors are more expensive, but faster, than PMOS transistors.

How the Elliott 803 transistorized computer works

Diagram of a germanium crystal lattice showing how the absence of an electron, called a hole, moves through the structure as electrons jump between atoms, with arrows and labels explaining each step.

A diagram showing a cross section of an n-p-n transistor with labeled gate, source, and drain on the left, and its electronic circuit symbol with the same labels on the right.

MESFET transistorIn a metal-semiconductor field-effect transistor (MESFET), current is normally on (used to represent “true” or “1”). A secondary voltage is applied to the gate to deplete charge carriers beneath it, thereby pinching off the current, or changing the state to off (“false” or “0”).

A line graph illustrating Moore's law, showing the exponential increase in the number of transistors on computer processors from 1970 to 2005, with key Intel processors labeled along the curve.

At a Glance

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Oct. 22, 2026 •History

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Single 2D crystal transforms into transistor with built-in insulation and electrical contacts • Oct. 15, 2026, 4:40 PM ET (Phys.org)

transistor, semiconductor device for amplifying, controlling, and generating electrical signals. Transistors are the active components of integrated circuits, or “microchips,” which often contain billions of these minuscule devices etched into their shiny surfaces. Deeply embedded in almost everything electronic, transistors have become the nerve cells of the Information Age.

There are typically three electrical leads in a transistor, called the emitter, the collector, and the base—or, in modern switching applications, the source, the drain, and the gate. An electrical signal applied to the base (or gate) influences the semiconductor material’s ability to conduct electrical current, which flows between the emitter (or source) and collector (or drain) in most applications. A voltage source such as a battery drives the current, while the rate of current flow through the transistor at any given moment is governed by an input signal at the gate—much as a faucet valve is used to regulate the flow of water through a garden hose.

The first commercial applications for transistors were for hearing aids and “pocket” radios during the 1950s. With their small size and low power consumption, transistors were desirable substitutes for the vacuum tubes (known as “valves” in Great Britain) then used to amplify weak electrical signals and produce audible sounds. Transistors also began to replace vacuum tubes in the oscillator circuits used to generate radio signals, especially after specialized structures were developed to handle the higher frequencies and power levels involved. Low-frequency, high-power applications, such as power-supply inverters that convert alternating current (AC) into direct current (DC), have also been transistorized. Some power transistors can now handle currents of hundreds of amperes at electric potentials over a thousand volts.

By far the most common application of transistors today is for computer memory chips—including solid-state multimedia storage devices for electronic games, cameras, and MP3 players—and microprocessors, where millions of components are embedded in a single integrated circuit. Here the voltage applied to the gate electrode, generally a few volts or less, determines whether current can flow from the transistor’s source to its drain. In this case the transistor operates as a switch: if a current flows, the circuit involved is on, and if not, it is off. These two distinct states, the only possibilities in such a circuit, correspond respectively to the binary 1s and 0s employed in digital computers. Similar applications of transistors occur in the complex switching circuits used throughout modern telecommunications systems. The potential switching speeds of these transistors now are hundreds of gigahertz, or more than 100 billion on-and-off cycles per second.

Development of transistors

The transistor was invented in 1947–48 by three American physicists, John Bardeen, Walter H. Brattain, and William B. Shockley, at the American Telephone and Telegraph Company’s Bell Laboratories. The transistor proved to be a viable alternative to the electron tube and, by the late 1950s, supplanted the latter in many applications. Its small size, low heat generation, high reliability, and low power consumption made possible a breakthrough in the miniaturization of complex circuitry. During the 1960s and ’70s, transistors were incorporated into integrated circuits, in which a multitude of components (e.g., diodes, resistors, and capacitors) are formed on a single “chip” of semiconductor material.

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Inventors and Inventions

Motivation and early radar research

Electron tubes are bulky and fragile, and they consume large amounts of power to heat their cathode filaments and generate streams of electrons; also, they often burn out after several thousand hours of operation. Electromechanical switches, or relays, are slow and can become stuck in the on or off position. For applications requiring thousands of tubes or switches, such as the nationwide telephone systems developing around the world in the 1940s and the first electronic digital computers, this meant constant vigilance was needed to minimize the inevitable breakdowns.

An alternative was found in semiconductors, materials such as silicon or germanium whose electrical conductivity lies midway between that of insulators such as glass and conductors such as aluminum. The conductive properties of semiconductors can be controlled by “doping” them with select impurities, and a few visionaries had seen the potential of such devices for telecommunications and computers. However, it was military funding for radar development in the 1940s that opened the door to their realization. The “superheterodyne” electronic circuits used to detect radar waves required a diode rectifier—a device that allows current to flow in just one direction—that could operate successfully at ultrahigh frequencies over one gigahertz. Electron tubes just did not suffice, and solid-state diodes based on existing copper-oxide semiconductors were also much too slow for this purpose.

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Crystal rectifiers based on silicon and germanium came to the rescue. In these devices a tungsten wire was jabbed into the surface of the semiconductor material, which was doped with tiny amounts of impurities, such as boron or phosphorus. The impurity atoms assumed positions in the material’s crystal lattice, displacing silicon (or germanium) atoms and thereby generating tiny populations of charge carriers (such as electrons) capable of conducting usable electrical current. Depending on the nature of the charge carriers and the applied voltage, a current could flow from the wire into the surface or vice-versa, but not in both directions. Thus, these devices served as the much-needed rectifiers operating at the gigahertz frequencies required for detecting rebounding microwave radiation in military radar systems. By the end of World War II, millions of crystal rectifiers were being produced annually by such American manufacturers as Sylvania and Western Electric.

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Development of transistors

Motivation and early radar research