A semiconductor device includes: a first stack structure; a second stack structure adjacent to the first stack structure in a first direction; a first insulating layer including protrusion parts protruding in a second direction intersecting the first direction and including a concave part defined between the protrusion parts; and a second insulating layer located between the first stack structure and the second stack structure, the second insulating layer inserted into the concave part and the second insulating layer in contact with at least one protrusion part among the protrusion parts.