semi + conductor

The word 'semiconductor' is a straightforward Latin compound: semi (half) plus conductor (something that carries). In 1874, Karl Ferdinand Braun discovered that certain materials—crystals of galena, silicon, germanium—conducted electricity in only one direction. He called this the rectifier effect. The material wasn't a proper conductor like copper, and it wasn't an insulator like rubber. It was something in between.

For decades, this property was a curiosity. Then, in 1947, three physicists at Bell Labs—William Shockley, John Bardeen, and Walter Brattain—built a device from a chunk of germanium that could amplify electrical signals. They called it a transistor. A transistor is a semiconductor sandwiched between three terminals, designed so that a small voltage at one terminal controls the flow of current between the other two. This was the first solid-state amplifier.

The transistor was transformative. Radios had used vacuum tubes—fragile, hot, power-hungry. Transistors were solid, reliable, and used almost no power. By the 1960s, transistors had replaced tubes in everything. But transistors couldn't shrink much further. Then, in 1958, Jack Kilby at Texas Instruments invented the integrated circuit: thousands of transistors on a single chip of semiconductor material. Moore's Law—the doubling of transistor density every two years—began.

Today, a single smartphone contains billions of transistors. Modern processors have transistors so small that the width is measured in nanometers—ten atoms across. Every transistor depends on the semiconductor property discovered by accident in 1874: a material that's neither conductor nor insulator, but something that responds to control.