PURPOSE: To enable to realize the semiconductor integrated circuit of a high density and high speed by using an MOS-type Tr.

CONSTITUTION: The source 4, drain 5, and gate 7 constitute the N type MOS transistor; on irradiation of a depletion layer 8 in the neighborhood of the drain with light, the electron-hole pairs are generated in the depletion layer 8, and the electrons are absorbed in the drain direction, while most of the holes diffuses into a P type region 2, and then absorbed to an electrode 3 formed by the side of the source. At this time, the potential immediately under the source 9 becomes higher than that of the electrode 3 by the resistance existent in the P type region 2, the P-N junction formed between the source 4 and the region 2 is biased in a forward direction, resulting in the flow of current 10. On the other hand, the variation in potential of the P type region 9 immediately under the source increases also the channel curret of the MOS transistor. Next, part of the currents 10 and 11 promotes the generation of new electron-hole pairs in the depletion layer 8 of the drain. The element constituting an amplifier of positive feedback is a piece of MOS Tr, the occupation area of which is extremely small.