A semiconductor device that is miniaturized and highly integrated is provided. One embodiment of the present invention is a semiconductor device including a first insulator, a second insulator, a first conductor, a second conductor, and a semiconductor layer; the first insulator includes an opening exposing the semiconductor layer; the first conductor is provided in contact with the semiconductor layer at a bottom of the opening; the second insulator is provided in contact with a top surface of the first conductor and a side surface in the opening; the second conductor is provided in contact with the top surface of the first conductor and in the opening with the second insulator therebetween; and the second insulator has a barrier property against oxygen.