A semiconductor device includes a silicon crystal layer on an insulating layer, the silicon crystal layer containing a crystal lattice mismatch plane, a memory cell array portion on the silicon crystal layer, the memory cell array portion including memory strings, each of the memory strings including nonvolatile memory cell transistors connected in series in a first direction, the memory strings being arranged in a second direction orthogonal to the first direction, the crystal lattice mismatch plane crossing the silicon crystal along the second direction without passing under gates of the nonvolatile memory cell transistors as viewed from a top of the silicon crystal layer, or crossing the silicon crystal along the first direction with passing under gates of the nonvolatile memory cell transistors as viewed from the top of the silicon crystal layer.