Specialty transistors are specialty or proprietary products and accessories related to transistors. There are two basic types of specialty transistors: NPN transistors and PNP transistors. An NPN transistor is a two-junction semiconductor transistor or bipolar transistor with an n-type collector, an emitter, and a p-type base. It uses p-type material between two regions of n-type material. A PNP transistor is a two-junction transistor with a p-type collector, an emitter, and an n-type base, which uses n-type semiconductor material between two regions of p-type material. Both NPN and PNP transistors are a type of power transistor used for low audio (noise) or general-purpose applications.