PURPOSE: To make hFE of an NPN transistor in an equivalent circuit large, and increase the switching speed, by applying a special I2L structure.

CONSTITUTION: On two parts of substrate 11, P-type diffusion layers 1 are formed, and in one P-type diffusion layer, an N-type layer 2 is formed, in which an N+ type diffusion layer 3 is formed. Further, in an insulating layer 12 on the N+ type diffusion layer 3, an aperture 5 is made, and here a metal electrode 6 is arranged to be applied to an output terminal. In the insulating layer 12 on the one P-type diffusion layer 1, an aperture 7 is made and here an electrode 8 is arranged to be applied to an input terminal. In the insulating layer 12 on the other P-type diffusion layer 1, an aperture 10 is made and here an electrode 9 is arranged to be applied to an injector. As the N-type diffusion layer 2 exisits in the P-type diffusion layer 1, hFE of an NPN transistor in an equivalent circuit becomes large, and so that switching speed is increased.