According to one embodiment, a semiconductor device includes a first semiconductor layer including a nitride semiconductor, a first electrode separated from the first semiconductor layer in a first direction, and a first insulating film including silicon and oxygen and being provided between the first semiconductor layer and the first electrode. The first insulating film has a first thickness in the first direction. The first insulating film includes a first position, and a distance between the first position and the first semiconductor layer is ½ of the first thickness. A first hydrogen concentration of hydrogen at the first position is 2.5×1019 atoms/cm3 or less.