A back-surface-incidence semiconductor light element includes: a semiconductor substrate of a first conductivity type; a first semiconductor layer of a first conductivity type on the semiconductor substrate; a light absorbing layer on the first semiconductor layer; a second semiconductor layer on the light absorbing layer; and an impurity diffusion region of a second conductivity type in a portion of the second semiconductor layer. A region including a p-n junction between the first semiconductor layer and the impurity diffusion region, and extending through the light absorbing layer, is a light detecting portion that detects light incident on a back surface of the semiconductor substrate. A groove in the back surface of the semiconductor substrate surrounds the light detecting portion, as viewed in plan.