One of the key inventions in the history of electronics, and in fact one of the most important inventions over period, was the transistor. It was invented by Bell Laboratories in 1984. In sort, a transistor is a device that conducts a variable amount of electricity through it , depending on how much electricity is input to it. In other words, it is a digital switch. However,unlike the vacuum tube, it is solid state. This means that it doesn’t change its physical form as it switches. There are no moving parts in a transistor.