Provided is a transistor with small parasitic capacitance or high frequency characteristics or a semiconductor device including the transistor. An oxide semiconductor film includes a first region in contact with a first conductive film, a second region in contact with a first insulating film, a third region in contact with a third insulating film, a fourth region in contact with a second insulating film, and a fifth region in contact with a second conductive film. The first insulating film is positioned over the first conductive film and the oxide semiconductor film. The second insulating film is positioned over the second conductive film and the oxide semiconductor film. The third insulating film is positioned over the first insulating film, the second insulating film, and the oxide semiconductor film. The third conductive film and the oxide semiconductor film partly overlap with each other with the third insulating film provided therebetween.