Uni Junction Transistor (UJT)
Basically, it is a three terminal
silicon diode. As the name indicates, it has only one pn junction. It differs
from an ordinary diode in that it has three terminals and it differs from a FET
in that it has no ability to amplify. However, it has the ability to control a
large a.c. power with a small signal. It also exhibits a negative resistance
characteristics which makes it useful as an oscillator.