Here, at last, the star of the modern chip walks on stage. The MOSFET — the metal-oxide-semiconductor field-effect transistor. The name is a mouthful, but the structure is simple.

Take a p-type silicon substrate and build two n-type regions in it, spaced apart. One is the source, the other the drain. Across the surface between them, lay down a thin insulating film (an oxide), and put an electrode on top of it. That electrode is the gate.