Abstract: A semiconductor light-detecting device includes: a semi-insulating substrate; and n light-detecting elements (n is a natural number equal to or larger than 4) electrically isolated from each other and on the semi-insulating substrate. Each light-detecting element includes a conductive layer of a first conductivity type, a light absorption layer, a window layer, and an impurity diffusion region of a second conductivity type, which are laminated, one on another, on the semi-insulating substrate. The light absorption layer is a photoelectrical converter. The impurity diffusion region is located in part of the window layer and serves as a light-detecting section. A part of the conductive layer and the light absorption layer use the same material. The n light-detecting elements are not all located on a common straight line.