Patent ID: 8716712

Claim:
A semiconductor device comprising: a light-receiving element configured to convert light into an electric signal; an insulating film over the light-receiving element; a first transistor configured to transfer the electric signal, one of a source and a drain of the first transistor being electrically connected to an output terminal of the light-receiving element; a second transistor configured to amplify the transferred electric signal, a gate of the second transistor being electrically connected to the other of the source and the drain of the first transistor; and a third transistor configured to control reading of an output signal generated by the second transistor, one of a source and a drain of the third transistor being electrically connected to one of a source and a drain of the second transistor, wherein the first transistor comprises an oxide semiconductor layer comprising the source and the drain, wherein the entire oxide semiconductor layer is provided over the insulating film and overlaps with the insulating film, wherein a gate of the third transistor extends over the light-receiving element, and wherein the first transistor is provided over the second transistor with the insulating film provided therebetween.