PURPOSE: To obtain a highly reliable, high-writing-speed, and electrically writable semiconductor device, by using a polysilicon diode with p-n junction.

CONSTITUTION: In the p region 3 of a stray-current preventive diode, a window is formed in an insulating film 2, and a polysilicon diode with p-n junction is formed covering the window with a diffused p type region 1' and the remaining part with a diffused n type region. As the reverse current of this polysilicon diode is increased, the diode characteristics change into resistance characteristics and information is written rapidly on a fuse basis according to a sudden rise in temperature due to the reverse current without fusing metal, and no residue generated in melting a metal, etc., owing to destruction inside of crystal near the p-n junction is generated, so that the reliability does not lower.