Disclosed is a semiconductor device comprising a substrate including a cell array region and a connection region, an electrode structure extending in a first direction on the substrate and including vertically stacked electrodes having pad sections arranged stepwise on the connection region, a first contact plug connected to a first one of the pad sections, a pair of first vertical structures that penetrate the first one of the pad sections and are spaced apart from each other in a first direction by a first distance, a second contact plug connected to a second one of the pad section and having a vertical length that is greater than that of the first contact plug, and a pair of second vertical structures that penetrate the second one of the pad sections and are spaced apart from each other in the first direction by a second distance that is greater than the first distance.