A semiconductor display device using a light-emitting element, which can suppress luminance unevenness among pixels due to the potential drop of a wiring, is provided. Power supply lines to which a power supply potential is supplied are electrically connected to each other in a display region where a plurality of pixels are arranged. Further, an interlayer insulating film is formed over a wiring (an auxiliary power supply line) for electrically connecting the power supply lines to each other in the display region and a gate electrode of a transistor included in a pixel; and the power supply lines are formed over the interlayer insulating film which is formed over the auxiliary power supply line and the gate electrode. Furthermore, a wiring (an auxiliary wiring) formed over the interlayer insulating film is electrically or directly connected to the auxiliary power supply line.