In one embodiment, a semiconductor device includes electrode layers and insulating layers alternately provided on a substrate and stacked in a first direction perpendicular to a surface of the substrate, and semiconductor layers provided in the electrode layers and insulating layers, extending in the first direction, and adjacent to each other in a second direction parallel to the surface of the substrate. The device further includes first and second charge trapping layers provided between the semiconductor layers and electrode layers sandwiching the semiconductor layers in a third direction parallel to the surface of the substrate. The device further includes insulators provided between the semiconductor layers being adjacent to each other in the second direction, and including a first insulator having a first width, and a second insulator having a second width longer than the first width and having nitrogen concentration different from that in the first insulator.