A memory device includes a pair of common source lines disposed on a substrate spaced apart from each other and extended in a first direction; a plurality of ground select lines disposed between the pair of common source lines, extended in the first direction, and disposed on the same level; a plurality of word lines disposed on the plurality of ground select lines between the pair of common source lines, extended in the first direction, and disposed on the same level, at least a portion of the plurality of word lines being connected by a connection electrode; and a plurality of first separation insulating patterns disposed between individual ground select lines of a portion of the plurality of ground select lines and extended in the first direction. The at least portion of the plurality of word lines is connected by a connection electrode.