Transistors are made of materials like silicon or germanium that are capable of allowing electrical current to flow through them in a controlled manner. The materials of transistors are doped, or “treated,” with impurities to create a structure called a p-n junction. In this case, “p” stands for positive and the “n” stands for negative. These notations refer to the type of dopant atoms (impurities) that have been added to the semiconductor material.

The most common type of transistor is the metal-oxide-semiconductor field-effect transistor (MOSFET), which is widely used in electronic devices such as computers, smartphones and televisions.

Components of a Transistor

A transistor consists of three main parts: the emitter, the base and the collector. The emitter serves as the source of electrons, the collector as the drain and the base as the control terminal.

More From This ExpertWhat Is the Dielectric Constant?


How Do Transistors Work?

When a small current flows through the base, it controls the flow of a much larger current between the emitter and the collector. This is due to the fact that the base-emitter junction is forward-biased, thereby allowing electrons to flow from the emitter to the base. The base-collector junction is reverse-biased, which means that electrons are prevented from flowing from the base to the collector. However, when a current flows through the base it opens up the base-collector junction and allows electrons to flow from the emitter to the collector.

This process allows the base to control the flow of current between the emitter and collector so we may use the transistor in a variety of ways.

Transistor diagram of a transistor and its parts as described abvoe
Typical structure of a transistor consisting of an emitter, collector and base. | Image: Shutterstock


Why Do We Use Transistors?

A transistor can act as a switch or gate for electronic signals. In practice this means we use transistors as electronic switches that turn electronic circuits on or off. This is a basic function that we use in digital logic circuits, such as those found in computers, where we use transistors to represent the ones and zeros of binary code.

We can also use transistors to control the power supply to different electronic components. The transistor acts as a switch to turn on and off the current flow. In addition, we can use transistors to adjust the voltage level, which allows for the efficient use of power in electronic devices.

One of the most important uses of transistors is as an amplifier. We can use transistors to amplify weak signals, such as the output from a microphone, to levels that can drive a loudspeaker.

Transistors Explained — How Transistors Work. | Video: The Engineering Mindset


What Are the 2 Main Types of Transistors?


In a BJT, the base-emitter junction is forward-biased by a small current. This configuration allows electrons to flow from the emitter to the base. The base-collector junction is reverse-biased, thereby acting as a barrier to the flow of electrons. However, the forward-biased base-emitter junction allows a small number of electrons to flow across the base-collector junction. This process creates a small current flow between the collector and emitter terminals that’s controlled by the base current.

Looking for More on Physics? We Got You.What Is an EMP?



In an FET, the gate terminal is separated from the channel by an insulating material. Applying a voltage to the gate terminal creates an electric field that can attract or repel the free electrons in the channel. This process changes the conductivity of the channel and thus controls the flow of current between the source and drain terminals. FETs have high input impedance, which means they draw very little current from the input signal.

In this way, transistors act like a switch, or an amplifier, depending on how they’re connected and how much current flows through them. The input current controls the output current, which we can use to amplify or switch signals.


Why Are Transistors Important?

Transistor image of blue transistors on a bright green circuit board
The image shows a circuit board containing transistors. | Image: Shutterstock

Transistors form the basic building blocks of modern electronics. They are versatile devices that can act as switches, amplifiers and signal regulators, thereby enabling the processing and storage of digital information. The widespread use of transistors in electronic devices has greatly impacted our daily lives by enabling modern communication, entertainment, transportation and healthcare technologies. For example, transistors have made it possible to miniaturize electronic circuits, leading to the creation of portable devices such as smartphones, laptops and wearable technology.

If transistors were never invented, our world would be very different. It’s likely that the computer revolution and the rapid advancements in electronics wouldn’t have happened, as transistors are a key component in digital circuits and modern computing. This would have slowed down technological advancements in fields such as communication, entertainment, transportation and healthcare. Electronic devices would have been much larger, slower and less efficient. Meanwhile, portable devices such as smartphones, laptops and wearable technology wouldn’t exist at all. 

Learn More With Built In’s Tech DictionaryWhat Is an Electrical Charge?


Examples of Transistors

Transistors are used in a wide variety of electronic devices and equipment, here are some common applications:

  • Computers: Transistors are a fundamental building block of modern computers. We use them in digital logic circuits, memory chips and microprocessors, which are all crucial components of a computer.
  • Cell Phones: In cell phones, transistors amplify signals and control the power supply to different components. They also play a role in the phone's processing power and memory capacity.
  • Automotive: Modern cars and trucks use transistors for engine control, power inverters for electric drives, power windows and other electronic systems. Transistors play a vital role in the electric vehicle market as they control the flow of electricity in the car's power electronic systems, thereby allowing for efficient conversion and distribution of power.
  • Space and Military Applications: Transistors’ small size, low power consumption and high-performance characteristics make them ideal for use in satellites, missiles and other electronic systems used for defense and exploration.
Expert Contributors

Built In’s expert contributor network publishes thoughtful, solutions-oriented stories written by innovative tech professionals. It is the tech industry’s definitive destination for sharing compelling, first-person accounts of problem-solving on the road to innovation.

Learn More

Great Companies Need Great People. That's Where We Come In.

Recruit With Us