A semiconductor device comprising: a driver circuit including a first transistor and a pixel including a second transistor over one substrate, wherein the first transistor and the second transistor each comprise: a gate electrode layer (411, 421); a gate insulating layer over the gate electrode layer (411, 421); an oxide semiconductor layer (412, 422) over the gate insulating layer; a source electrode layer (415a, 409a) over the oxide semiconductor layer (412, 422); a drain electrode layer (415b, 409b) over the oxide semiconductor layer (412, 422); and an oxide insulating layer over the gate insulating layer, the oxide semiconductor layer (412, 422), the source electrode layer (415a, 409a), and the drain electrode layer (415b, 409b), the oxide insulating layer being in contact with at least a part of the oxide semiconductor layer (412, 422) between the source electrode layer (415a, 409a) and the drain electrode layer (415b, 409b), wherein the gate electrode layer, the gate insulating layer, the oxide semiconductor layer (412, 422), the source electrode layer, the drain electrode layer, and the oxide insulating layer of the second transistor each have a light-transmitting property, and wherein the source electrode layer and the drain electrode layer of the first transistor are formed using a material different from that of the source electrode layer and the drain electrode layer of the second transistor and have lower resistance than that of the source electrode layer and the drain electrode layer of the second transistor, further comprising an oxide conductive layer between the oxide semiconductor layer (412, 422) and each of the source and drain electrode layers (415a, 415b) of the first transistor, wherein the oxide conductive layer is formed using the same material as that of the source and drain electrode layers (409a, 409b) of the second transistor. a driver circuit including a first transistor and a pixel including a second transistor over one substrate, wherein the first transistor and the second transistor each comprise: a gate electrode layer (411, 421); a gate insulating layer over the gate electrode layer (411, 421); an oxide semiconductor layer (412, 422) over the gate insulating layer; a source electrode layer (415a, 409a) over the oxide semiconductor layer (412, 422); a drain electrode layer (415b, 409b) over the oxide semiconductor layer (412, 422); and an oxide insulating layer over the gate insulating layer, the oxide semiconductor layer (412, 422), the source electrode layer (415a, 409a), and the drain electrode layer (415b, 409b), the oxide insulating layer being in contact with at least a part of the oxide semiconductor layer (412, 422) between the source electrode layer (415a, 409a) and the drain electrode layer (415b, 409b), a gate electrode layer (411, 421); a gate insulating layer over the gate electrode layer (411, 421); an oxide semiconductor layer (412, 422) over the gate insulating layer; a source electrode layer (415a, 409a) over the oxide semiconductor layer (412, 422); a drain electrode layer (415b, 409b) over the oxide semiconductor layer (412, 422); and an oxide insulating layer over the gate insulating layer, the oxide semiconductor layer (412, 422), the source electrode layer (415a, 409a), and the drain electrode layer (415b, 409b), the oxide insulating layer being in contact with at least a part of the oxide semiconductor layer (412, 422) between the source electrode layer (415a, 409a) and the drain electrode layer (415b, 409b), wherein the gate electrode layer, the gate insulating layer, the oxide semiconductor layer (412, 422), the source electrode layer, the drain electrode layer, and the oxide insulating layer of the second transistor each have a light-transmitting property, and wherein the source electrode layer and the drain electrode layer of the first transistor are formed using a material different from that of the source electrode layer and the drain electrode layer of the second transistor and have lower resistance than that of the source electrode layer and the drain electrode layer of the second transistor, further comprising an oxide conductive layer between the oxide semiconductor layer (412, 422) and each of the source and drain electrode layers (415a, 415b) of the first transistor, wherein the oxide conductive layer is formed using the same material as that of the source and drain electrode layers (409a, 409b) of the second transistor.