Yes. It's a sandwich of substances, one type of substance in the center and another type on each side. All the substances are doped with something. The purpose is to amplify electrical signals (or it can also work as an on-off switch--same function, different way of using it). The voltage applied to the center substance determines how much electricity passes across the other two substances. Transistors are used in virtually all electronics and are the basis for all microprocessors. Before transistors, this function was accomplished by vacuum tubes, which were much bigger, slower, less efficient, and more prone to burnout.

Transistors in modern CPUs are the size of microns. They're so small and there are so many of them (tens of billions) in a single CPU that the factories that create them cost billions of dollars each. In other circuits they can be big enough to grab between your fingers.