Which electronic component can be classified as NPN or PNP?

A transistor can be classified as NPN or PNP. These labels describe the arrangement of n-type and p-type semiconductor regions in a bipolar junction transistor, or BJT.

An NPN transistor has an n-type emitter, a p-type base, and an n-type collector. A PNP transistor reverses that pattern: p-type emitter, n-type base, and p-type collector. Both have three terminals—emitter, base, and collector—and can amplify or switch electrical signals.

The letters refer to the semiconductor doping pattern, not to different component families. NPN devices generally conduct through electrons, while PNP devices primarily involve holes. In circuit diagrams, the emitter-arrow convention is a useful memory aid: an NPN arrow points out, while a PNP arrow points in. Field-effect transistors are also transistors, but they are not normally classified as NPN or PNP.