On the front side of an n-type semiconductor substrate, p-type regions are two-dimensionally arranged in an array. A high-concentration n-type region and a p-type region are disposed between the p-type regions adjacent each other. The high-concentration n-type region is formed by diffusing an n-type impurity from the front side of the substrate so as to surround the p-type region as seen from the front side. The p-type region is formed by diffusing a p-type impurity from the front side of the substrate so as to surround the p-type region and high-concentration n-type region as seen from the front side. Formed on the front side of the n-type semiconductor substrate are an electrode electrically connected to the p-type region and an electrode electrically connected to the high-concentration n-type region and the p-type region.