When the transistor switches, the change in voltage alters the electronic properties of the material and determines whether or not electrons can flow through it.
Their job is to convert high-voltage alternating current from the mains into low-voltage direct current for mobile phones, laptops, iPods and other electronic gadgets.
Electronic chips consist of millions of transistors, each of which does one simple thing: it uses the voltage at one of its three junctions to decide whether or not to let current flow between the other two.