A semiconductor device includes a comprise a substrate including a main zone and an extension zone, vertical channels on the main zone, and an electrode structure including gate electrodes stacked on the substrate. The vertical channel structures extend in a first direction perpendicular to a top surface of the substrate. The gate electrodes include line regions and contact regions. The line regions extend from the main zone toward the extension zone along a second direction the second direction that is perpendicular to the first direction. The contact regions are on ends of the line regions and are thicker than the line regions. A spacing distance in the second direction between the contact regions is greater than a spacing distance in the first direction between the line regions.