Abstract: To reduce the required diffusion depth of impurities in manufacturing a protective diode for protecting an insulated gate transistor from overvoltage so that the diode can be easily built in a chip of the transistor. A plurality of p-type diode layers are built in by diffusion through the windows in an insulation film disposed on an n-type region into which a depletion layers spread when the vertical field effect transistor to be protected is turned off, and a diode terminal A is led out from an electrode film that is in electrical contact with the diode layers. This configuration prevents depletion layers, spreading from the diode layers into the semiconductor region by the applied overvoltage, from joining with each other, and sufficiently lowers the breakdown voltage of the protective diode with respect to the withstand voltage of the transistor 10 or 20 even when the diffusion depth of the diode layer is one order of magnitude shallower than in conventional devices.