TRIGGER ELEMENT

PURPOSE:To improve load resistance characteristic and to perform an ON operation by providing a short-circuiting electrode at a position reaching a depleted layer before a PN junction between a diffused layer and a semiconductor substrate is broken down by a reverse bias to be applied to the junction. CONSTITUTION:If a voltage is applied to electrodes 6a, 6b, a PN junction 7a is reversely biased, and a PN junction 7b is forwardly biased. When an applied voltage VR is low, only a leakage current of the junction 7a flows between the electrodes 6a and 6b to become an OFF state, and as the voltage VR is increased, a depleted layer 5a is extended. Its end reaches a short-circuiting electrode 4a, the electrodes 6a, 6b are forwardly biased to become an ON state. When the polarities of the electrodes 6a, 6b are replaced, the junctions 7a, b7 are forwardly and reversely biased to become the ON state. Thus, when they are reversely biased, it reaches a depleted layer before the junction is broken down. Then a trigger element obtains desirable characteristics to provide the ON operation without problem.