A semiconductor diode consists of a low resistivity n conductivity type semiconductor substrate, a high resistivity n conductivity type semiconductor layer, formed on the surface of the substrate, a high resistivity p conductivity type semiconductor layer, whose thickness is smaller than the diffusion length of electrons, formed on the n conductivity type layer, a metal electrode forming a Schottky barrier contact with the p conductivity type layer, and an electrode forming an ohmic contact with the substrate.