Patent ID: 8659523

Claim:
A semiconductor device comprising: a light-emitting element; a first transistor; a second transistor; and a third transistor, wherein one of a source and a drain of the first transistor is electrically connected to the light-emitting element, wherein the other of the source and the drain of the first transistor is electrically connected to one of a source and a drain of the second transistor, wherein a gate of the second transistor is electrically connected to one of a source and a drain of the third transistor, wherein the other of the source and the drain of the third transistor is electrically connected to a first line, wherein a gate of the first transistor is electrically connected to a second line, wherein the other of the source and the drain of the second transistor is electrically connected to a third line, wherein the third line comprises a conductive film, wherein the conductive film overlaps with a channel formation region of the first transistor, wherein the conductive film overlaps with a channel formation region of the second transistor, wherein a semiconductor film comprises the channel formation region of the first transistor and the channel formation region of the second transistor, and wherein a channel length of the first transistor is longer than a channel width of the first transistor.