A diode includes: a p-type semiconductor substrate; an n-type semiconductor layer; a p-type isolation region formed to surround a predetermined region of the n-type semiconductor layer on the p-type semiconductor substrate; an n-type buried layer formed across the p-type semiconductor layer and the n-type semiconductor layer within the predetermined region; an n-type collector wall formed in the n-type semiconductor layer; a p-type anode region and a plurality of n-type cathode regions formed in a diode formation region; and a p-type guard ring formed to surround the diode formation region in a region between the diode formation region of the surface layer of the n-type semiconductor layer and the p-type isolation region. A transistor for reducing a leakage current is formed by the p-type anode region, the p-type guard ring, and an n-type semiconductor between the p-type anode region and the p-type guard ring.