Transistors.

They are made from semiconductor materials and have three electrodes caled the base, the collector and the emitter. There are two types:

Each electrode is connected to a semiconductor material which releases electrons or acceps electrons.
I'm going to explain how transistors work:

⇒When there aren't electrons through the base, electrons cant pass from the collector to the emitter. This phase is called cut off.

⇒When electrons are passing through the base, electrons can pass from the collector and the emitter.
This phase is called saturation.

⇒When the flow of electrons is between cut off and saturation, the flow of electrons between the collector and the emitter is proportional. This phase is called active región.

Transistors are the basisc components of the microprocessors and memory circuits that are used in computers. This is called a transistor gain.