Home | Physics | What is a Transistor?-Definition, Types, Parts, Working, And Advantages

What is a Transistor?-Definition, Types, Parts, Working, And Advantages

August 27, 2022
written by Qamar Zaman

The transistor is a tiny semiconductor that helps to regulate or control the flow of current or voltage, amplifying electrical signals and acting as a switch or gate for them. Most transistors are made up of three layers, or terminals, of semiconductor material, with each layer able to carry a current.

What is a Transistor?

The transistor is a solid-state switch. A transistor is a three-terminal device used to amplify and control electronic signals. It can be used to amplify signals, switch currents, and block currents. 

Transistor Parts

A transistor is typically made up of three layers of semiconductor materials, or more specifically, terminals. These terminals help to make a connection to an external circuit and carry the current. By applying a voltage or current to any one pair of the transistor’s terminals, the current going through the other pair of terminals can be controlled. They are:


The base, indicated by the letter B, is the center terminal located between the emitter and the collector. Its doping is light, making it thin and its main purpose is to enable carriers to pass from the emitter to the collector.


The collector is responsible for collecting carriers from the emitter and delivering them to the base. The collector is moderately doped, which means it can handle more carriers than the emitter or base. It’s also larger in size than both the emitter and base.


The emitter, which is represented by the letter E, is of moderate size. It’s heavily doped because its primary responsibility is to provide a large number of carriers that will support the flow of electricity. The emitter emits electrons, which is why it’s called the emitter.

Types of Transistors

There are two main types of transistors: those that are used as switches, and those that are used as amplifiers.

  • Bipolar Junction Transistor (BJT)
  • Field Effect Transistor (FET)

Bipolar Junction Transistor (BJT)

Bipolar transistors get their name from the fact that they use both majority and minority carriers in order to conduct. The bipolar junction transistor, which was the first type of transistor to be mass-produced, is made up of two junction diodes.

You can create a bipolar transistor out of either a thin layer of p-type semiconductor sandwiched between two n-type semiconductors (an n–p–n transistor) or by using a thin layer of n-type semiconductor sandwiched between two p-type semiconductors (a p–n–p transistor). This construction produces two p–n junctions: a base-emitter junction and a base-collector junction. These two junctions are separated by a thin region of semiconductor known as the base region.

Field Effect Transistor (FET)

For FET, the three terminals are Gate, Source, and Drain. The voltage at the gate terminal controls the current between the source and the drain.

FET is a unipolar transistor that uses either an N-channel FET or P-channel FET for conduction. The main applications for FETs are low-noise amplifiers, buffer amplifiers, and analog switches.

The transistor have also some types that are mentioned below:

  • Optical Transistor
  • Diffusion Transistor
  • Avalanche Transistor
  • Schottky Transistor
  • Darlington Transistor
  • Heterojunction Bipolar Transistor
  • Junction FET Transistor
  • Dual Gate MOSFET
  • Multiple-Emitter Transistor

Transistor Working

A transistor can act as a switch or gate for electronic signals and can be opened and closed many times per second. It makes sure that the circuit is on if the current is flowing and off if it isn’t. All modern telecommunications systems use transistors in their circuits. Hundreds of gigahertz, or more than 100 billion on-and-off cycles per second, are some of the high switching speeds offered by circuits. Transistors can be combined to form a logic gate, which compares multiple input currents to provide different outputs.

Computers with logic gates are capable of making simple decisions. The foundations of modern-day computing and computer programs are found in these techniques. The amplification of electronic signals is an important role played by transistors. In radio applications, where the received electrical signal may be weak due to disruptions, amplification is required to provide audible output. Transistors help amplify the signal by increasing its strength.


The main benefits of using transistors include their low cost and small size. They are also less sensitive to mechanical issues and have a very long lifespan. Unlike other types of transistors, transistors do not require any power to operate and can be switched very quickly. Additionally, they are more efficient than other types of transistors, making them ideal for use in developing integrated circuits.

File Under: