A semiconductor device includes a substrate, a plurality of insulating layers vertically stacked on the substrate, a plurality of channels arranged in vertical openings formed through at least some of the plurality of insulating layers, and a plurality of portions alternatingly positioned with the plurality of insulating layers in the vertical direction. At least some of the portions are adjacent corresponding channels of the plurality of channels. Each of the portions includes a conductive barrier pattern formed on an inner wall of the portion, a filling layer pattern positioned in the portion on the conductive barrier pattern, and a gate electrode positioned in a remaining area of the portion not occupied by the conductive barrier or filling layer pattern.