Transistors and other semiconductor devices
Rhys Lewis · 1983
The semiconductor component with three electrodes is called a transistor. There are two types: the bipolar transistor, which uses both electron and hole conduction; and the unipolar or field-effect transistor (FET), which uses either electron or hole conduction. (It should be remembered that hole conduction also uses electrons as charge-carriers but that these electrons are those normally in the bond between atoms; electron conduction uses 'free' electrons, which do not necessarily move from one atom to the one adjacent.)