According to one embodiment, a semiconductor device includes an insulating substrate including a pixel area and a peripheral circuit area around the pixel area, a first insulating layer which is provided on the insulating substrate and includes at least nitrogen, a second insulating layer at least provided on the first insulating layer of the peripheral circuit area, a first thin-film transistor which is provided above the first insulating layer of the pixel area and includes a first oxide semiconductor layer, and a second thin-film transistor which is provided on the second insulating layer of the peripheral circuit area and includes a second oxide semiconductor layer. The second insulating layer in the pixel area is thinner than that in the peripheral circuit area.