A gate electrode, a first insulating film thereover, an oxide semiconductor film thereover, a source electrode and a drain electrode thereover, and a second insulating film thereover are included. The source and the drain electrodes each include a first conductive film, a second conductive film over and in contact with the first conductive film, and a third conductive film over and in contact with the second conductive film. The second conductive film includes copper. The first and the third conductive films each include an oxide conductive film. An end portion of the first conductive film includes a region located outward from an end portion of the second conductive film. The third conductive film covers a top surface and a side surface of the second conductive film and includes a region in contact with the first conductive film.