On the surface side of an n-type semiconductor substrate (5), p-type regions (7) are arrayed two-dimensionally. A heavily doped n-type region (9) and a p-type region (11) are arranged between adjacent p-type regions (7). The heavily doped n-type region (9) is formed to surround the p-type region (7), when viewed from the surface side, by diffusing n-type impurities from the surface side of the substrate (5). The p-type region (11) is formed to surround the p-type region (7) and the heavily doped n-type region (9), when viewed from the surface side, by diffusing p-type impurities from the surface side of the substrate (5). On the surface side of the n-type semiconductor substrate (5), an electrode (15) being connected electrically with the p-type regions (7) and an electrode (19) being connected electrically with the heavily doped n-type region (9) and the p-type region (11) are formed. A semiconductor photodetecting element and a radiation detector, in which crosstalk can be suppressed well and inflow of carriers to an adjacent photodiode can be suppressed even if some photodiode is brought into electrically floating state due to initial connection error or damage of a connecting point due to temperature cycle, are thereby realized. |