To improve the reliability of a semiconductor device including a low-resistance material such as copper, aluminum, gold, or silver as a wiring. Provided is a semiconductor device including a pair of electrodes electrically connected to a semiconductor layer which has a stacked-layer structure including a first protective layer in contact with the semiconductor layer and a conductive layer containing the low-resistance material and being over and in contact with the first protective layer. The top surface of the conductive layer is covered with a second protective layer functioning as a mask for processing the conductive layer. The side surface of the conductive layer is covered with a third protective layer. With this structure, entry or diffusion of the constituent element of the pair of conductive layers containing the low-resistance material into the semiconductor layer is suppressed.