To provide a semiconductor device including a planar transistor having an oxide semiconductor and a capacitor. In a semiconductor device, a transistor includes an oxide semiconductor film, a gate insulating film over the oxide semiconductor film, a gate electrode over the gate insulating film, a second insulating film over the gate electrode, a third insulating film over the second insulating film, and a source and a drain electrodes over the third insulating film; the source and the drain electrodes are electrically connected to the oxide semiconductor film; a capacitor includes a first and a second conductive films and the second insulating film; the first conductive film and the gate electrode are provided over the same surface; the second conductive film and the source and the drain electrodes are provided over the same surface; and the second insulating film is provided between the first and the second conductive films.