Provided is a semiconductor device having a large threshold voltage. The semiconductor device comprises: a first conductor disposed on a substrate; a first insulator disposed on the first conductor; a first oxide disposed in contact with the upper surface of the first insulator; a second insulator disposed in contact with the upper surface of the first oxide; a second oxide disposed on the second insulator; a third insulator disposed on the second oxide; and a second conductor disposed on the third insulator, wherein a mixed layer is formed between the first insulator and the first oxide, the mixed layer includes at least one of the atoms contained in the first insulator and at least one of the atoms contained in the first oxide, and the mixed layer has a negative fixed charge.