PURPOSE: To increase the breakdown rating with no sacrifice of the high-speed and high frequency characteristics plus the DC current amplification factor by projecting the peripheral part of the emitter layer into the base layer deeper than the central part.

CONSTITUTION: N+-type collector layer 4 is formed through diffusion on the back of N-type Si substrate 3 which becomes the collector layer, and P-type base layer 5 is formed through diffusion on the surface. Then the N-type impurity is diffused into layer 5 to form N-type emitter layer 6. In this case, peripheral part 6a of layer 6 is formed deeper by 5μm or more than central part 6b which is to be formed next to secure the prescribed pattern. After this, Al emitter electrode 1, Al base electrode 2 and collector electrode 7 are attached to region 6, layer 5 and layer 4 respectively. As a result, a difference of 1 or 2 digits is caused for the ampification factor between part 6a and 6b of layer 6. Owing to this difference, the current never enters the inside from part 6a at the turn-off time, thus increasing the rating to the breakdown.