A semiconductor device having stable electrical characteristics is provided. A semiconductor device that can be miniaturized or highly integrated is provided. One embodiment of the present invention includes a transistor including an oxide, a first barrier layer over the transistor, and a second barrier layer in contact with the first barrier layer. The oxide is in contact with an insulator including an excess-oxygen region. The insulator is in contact with the first barrier layer. The first barrier layer has a thickness greater than or equal to 0.5 nm and less than or equal to 1.5 nm. The second barrier layer is thicker than the first barrier layer.