The Uni-junction Transistor (UJT) is a solid-state, three-terminal device.UJT is constructed using P-type and N-type semiconductor materials. It has a single PN-junction formed within the main N-type channel. 

The transistor consists of three layers: NPN or PNP. The collector current (Ic) is dependent on the base current (IB). A change in base current IB results in an amplified change in collector current Ic. The ratio of these currents ranges from 15 to 100 and called beta ẞ.

Introduction to power electronic , power converter circuits, power semi conductor devices and brief comparison between types of power diodes