What are the two basic types of bipolar transistors?

Bipolar Junction Transistors (BJTs) are made by sandwiching one type of doped semiconductor material between two layers of the opposite type. This creates two distinct configurations based on whether the P-type or N-type material is in the middle. An NPN transistor has a P-type base between N-type emitter and collector layers, while a PNP transistor has an N-type base between P-type emitter and collector layers. These are the two basic types of bipolar transistors. Distractors like "P channel and N channel" apply to Field-Effect Transistors (FETs), not bipolar transistors. Diodes and triodes refer to two-terminal semiconductors and older vacuum tube technologies, respectively.