A semiconductor device with a high on-state current is provided. The semiconductor device includes a first insulator over a substrate, an oxide over the first insulator, a second insulator over the oxide, a conductor overlapping with the oxide with the second insulator therebetween, a third insulator in contact with a top surface of the oxide, a fourth insulator in contact with a top surface of the third insulator, a side surface of the second insulator, and a side surface of the conductor, and a fifth insulator in contact with a side surface of the fourth insulator, a side surface of the third insulator, and the top surface of the oxide. The third insulator has a lower oxygen permeability than the fourth insulator.