What Is a Semiconductor?

A semiconductor is a material that conducts electricity better than an insulator such as glass, but far less well than a metal such as copper. What makes it useful is that its conductivity can be changed on purpose, by adding tiny amounts of other elements, by applying a voltage, or by light and heat.

Silicon is by far the most common semiconductor, because it is plentiful, forms a stable oxide and can be refined to extreme purity. Germanium, gallium arsenide, gallium nitride and silicon carbide fill more specialized roles.

The word is used in two ways. Strictly, it means the material. In everyday use, semiconductors also means the devices made from it, from single transistors to processors, memory and sensors, and the industry that makes them.

In a pure semiconductor crystal, almost every electron is held in a bond between atoms, so very little current flows. The energy needed to free an electron is called the band gap. It is small enough that heat, light or a voltage can free some electrons, but large enough that the material stays a poor conductor until that happens.

Doping changes that. Adding a trace of phosphorus gives the silicon spare electrons, making n-type material. Adding boron leaves gaps, called holes, that act as positive charges, making p-type material. Where p-type and n-type silicon meet, they form a p-n junction, which lets current flow one way but not the other. That is a diode.

Put the junctions together in the right pattern and you get a transistor: a switch with no moving parts that a small voltage turns on and off. The MOSFET transistor in modern chips switches billions of times a second, and every logic gate, memory cell and processor core is built from them.

The band gap decides much of how a material behaves. A wider band gap copes with higher voltages and temperatures, which is why silicon carbide and gallium nitride are taking over in power electronics and chargers.

Band gaps are quoted at room temperature and vary slightly with crystal structure.

A chip, or integrated circuit, starts as a thin wafer sliced from a single crystal of purified silicon. The wafer is built up in hundreds of steps: layers are deposited, patterned with light through a mask (photolithography), etched away and doped, until billions of transistors and the copper wiring between them are formed. The finished wafer is tested, cut into individual dies and packaged with the pins or solder balls that connect it to a circuit board.

Process names such as “3 nm” are now generation labels rather than the size of any one feature, but each new node still packs in more transistors and usually cuts power. A complete system on chip places processor cores, graphics, AI engines and I/O controllers on a single die or package.

For industrial equipment, how long a chip stays on sale matters as much as how fast it is. Consumer processors are often replaced within a year or two, while a control system, vehicle or medical device may be built and supported for ten years or more. Changing the processor mid-life can mean a new board, new drivers and requalification.

The 2020 to 2023 chip shortage showed the other risk: lead times on some processors, microcontrollers and power parts stretched to a year or more. Industrial buyers now plan supply as carefully as specification. Our guide to CPU generations and embedded processors covers how embedded roadmaps differ from consumer ones.

We supply industrial computers built on embedded-roadmap processors, with lifecycle support and last-time-buy planning as standard. Tell us how long your project needs to run, and we will recommend a processor family to match.