PURPOSE: To provide a phototransistor with improved switching speed in a saturated state of motion having a large quantity of incident light with no decrease in light receiving sensitivity.

CONSTITUTION: A phototransistor comprises a base diffusion layer 14 formed on a collector layer 13 connected to an exposed member 15, to which part of the collector layer 13 is pierced and exposed thereon, and a Schottky metal electrode 19 provided to form a Schottky barrier at the contact part with the collector layer 13. As a result, when the quantity of incident light is so large as to cause saturated motion, a forward current runs in the Schottky barrier, thus suppressing the forward current in the base collector junction. And implantation of minority carrier from the base diffusion layer 14 to the collector layer 13 is suppressed, reducing the storage electric charge at the collector layer 13 and the storage time and increasing switching speed. At this time, because the life time of the minority carrier in the collector layer 13 is not shortened, the light receiving sensitivity does not decrease.