A semiconductor device includes a light-receiving element which outputs electric charges in response to incident light, and a drive transistor which is gated by an output of the light-receiving element to generate a source-drain current in proportion to the incident light, wherein the drive transistor include a first gate electrode, a first channel region which is disposed under the first gate electrode, first source-drain regions which are disposed at respective ends of the first channel region and that have a first conductivity type, and a first channel stop region which is disposed on a side of the first channel region, and that separates the light-receiving element and the first channel region, the first channel stop region having a second conductivity type that is different from the first conductivity type.