Abstract: A semiconductor X-ray detector device has an i layer configured to substantially a circular cylindrical shape but not a conventional top-hat shape and a p layer provided to substantially cover the circumferential side of the i layer. Both an n+ layer and an n surface electrode are arranged smaller in the area than the bottom at the n surface electrode side of the i layer in order to expose the i layer entirely to the electric field E. Accordingly, the spectrum remains not fractured in the profile when the n+ layer and the n surface electrode are not greater in the area than 33% of the bottom at the n surface electrode side of the i layer, hence permitting the resolving power to stay high.