First and foremost, a semiconductor is a material, such as silicon, which has certain properties of conducting or resisting electrical currents.
Those properties can be used to amplify or switch electronic signals, creating atomic-size electrical switches (also called transistors). Their key function is the ability to control the flow of electrical currents.
Semiconductors can control electrical currents, emit light, store and compute data, or mix and transform signals. They come in numerous different forms, such as microprocessors, memory chips, sensors, LEDs and many more.
💡 A modern transistor is 10.000 times thinner than a human hair. There are up to 100 billion transistors on a high-end processor today.