PURPOSE: To simplify a manufacturing process, by making in an n type substrate a p+ type region whose concentration is lower at the surface and deep part of the substrate and maximum at an appropriate depth from the surface and by making an n+ type diffusion region to provide a p+-n+ junction.

CONSTITUTION: A p+ type diffusion layer 5 is produced in an n type Si substrate 1 so that the concentration of the layer is maximum at an appropriate depth (d) from the surface of the substrate and lower near the surface. An anode A is in contact with the peripheral part of the surface of a p- type diffusion layer 6 whose concentration is low and which contains the p+ type diffusion layer 5. An n+ type diffusion layer 2 is provided in a part of the p- type diffusion layer 6 so that the layer 2 extends from the surface of the layer 6 to the p+ type layer 5. A cathode K is provided in contact with the surface of the n+ type diffusion layer 2.