A display device comprising a transistor and a display element over the transistor, wherein the transistor includes a gate electrode on an insulating surface, a gate insulating layer on the gate electrode, and source/drain electrodes on the oxide semiconductor layer and the gate insulating layer, each including a first conductive layer containing nitrogen and a second conductive layer on the first conductive layer, and an insulating layer contains oxygen on the oxide semiconductor layer and the source/drain electrodes.