A semiconductor device includes a first barrier layer having a barrier property against oxygen and hydrogen over a substrate, a first insulator over the first barrier layer, a second insulator over the first insulator, a third insulator over the second insulator, a transistor including an oxide semiconductor over the third insulator, a fourth insulator including an oxygen-excess region over the transistor, and a second barrier layer having a barrier property against oxygen and hydrogen over the fourth insulator. The transistor includes a first conductor with oxidation resistance, a second conductor with oxidation resistance, and a third conductor with oxidation resistance, the second insulator includes a high-k material, the first barrier layer and the second barrier layer are in contact with each other in an outer edge of a region where the transistor is provided, and the transistor is surrounded by the first barrier layer and the second barrier layer.