A Building Block of Modern Tech

The transistor celebrated its 75th birthday in December 2022. One of its inventors, John Bardeen, spent most of his career at the University of Illinois Urbana-Champaign.

Spring 2023

It was co-invented by John Bardeen, a two-time Nobel laureate who was on the faculties of electrical & computer engineering and physics at the University of Illinois Urbana-Champaign from 1951 to his death in 1991. Although he was a theorist, his early training in electrical engineering allowed him to form close relationships with experimentalists and engineers. His strong understanding of both theoretical solid-state physics and engineering made him the right person at the right time in the story of the transistor.

John Bardeen demonstrating the transistor
John Bardeen demonstrating the resistor in December 1947, while working at Bell Labs. He and his colleagues Walter Brattain and William Shockley ushered in the era of solid state electronics (no vacuum tubes or moving parts) with their invention of the transistor, earning the team the 1956 Nobel Prize in physics.

He was recruited in 1945 to Bell Telephone Laboratories, where research seeking a replacement for the vacuum tube triode was being carried out. Since the 1910s, triodes’ ability to amplify weak electrical signals had made commercial telephone, radio, and sound recording possible, but they were large, inefficient, and unreliable. Some scientists thought that semiconductor devices could be strong candidates for alternatives because of the field effect, in which the surface electrical conductivity can be controlled with an applied voltage. 

When Bardeen arrived at Bell Labs, there had been little progress toward a practical device. He partnered with experimentalist Walter Brattain to study semiconductor surface effects. They eventually surmised that a small region with p-type conductivity would form on their n-type germanium wafer near a point of contact with gold foil. By applying a small voltage to the germanium, they could alter the number of positive charges, or electron holes, in the p-type region and change the flow of electrical current through the material. Modulating the applied voltage could then encode a signal in the passing current. 

Bardeen and Brattain were thus able to demonstrate semiconductor amplification on December 16, 1947. Their device was named the point-contact transistor. Although later semiconductor devices would be differently constructed, Bardeen and Brattain’s was the first proof-of-principle, heralding the era of modern electronics. They shared the 1956 Nobel Prize in physics with William Shockley, who had proposed the bipolar junction transistor, “for their researches on semiconductors and their discovery of the transistor effect.” 

Nick Holonyak, Jr., the inventor of the LED, was a graduate student (and later colleague) of Bardeen at the University of Illinois. He recalled a lecture on semiconductor physics in which Bardeen identified the discovery of electron hole behavior as the key insight leading to the first transistor. However, Bardeen, who was always careful to give others credit for their ideas, curiously failed to do so in this case. Holonyak concluded that the insight must have been Bardeen’s, and that Bardeen’s characteristic modesty extended even to his Nobel Prize-winning achievement.

What Transistors Have Made Possible
Over The Last 75 Years

Electrical Power

One of the transistor’s most common uses is in devices to regulate and convert between different forms of electrical power, from power lines to wall electricity to appliances and electronics. Without transistors, the electrical grid would be much denser and much less efficient.

Digital Computing

In addition to performing amplification, transistors can also be used as on/off switches. Digital computers use them to represent data in binary bits (0s and 1s). Turning transistors on and off is how our electronics perform millions, even billions, of calculations every second.


Because transistors are “material-level” devices, they can be made incredibly compact, allowing for micro- and nanoscale electronic chips. Without transistor-based microchips, computers would still fill entire rooms, and mobile telephones would be as large as backpacks.

Cellular Networks

Wireless communication depends on high-frequency radio waves that are controlled with high-speed transistors. Moving from the current 5G to a future 6G standard will require new kinds of transistors made from materials beyond silicon to achieve the even higher speeds that are needed.

Rechargeable Batteries

The battery arrays used in electric vehicles and other applications need to be carefully managed. Improper charging can lead to greatly reduced performance and even fires. Circuits that monitor and regulate everything from individual battery cells to the entire system are possible because of transistors.

Solar Panels

Solar cells produce DC power, but power lines require AC. An inverter is needed to convert one kind of power to the other, and inverters depend on transistors. Without them, our work towards renewable energy would look very different, if it would even be possible.

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This story was published March 1, 2023.

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