According to one embodiment, a semiconductor device includes a first insulating film formed of silicon nitride, a second insulating film disposed above the first insulating film and formed of silicon oxide, including a first region and a peripheral region surrounding the first region and thinner than the first region, an oxide semiconductor disposed on the second insulating film and intersecting the first region, a source electrode overlapping the peripheral region and a drain electrode overlapping the peripheral region. The first region is located between the source electrode and the drain electrode and separated from the source electrode and the drain electrode.