A three-dimensional semiconductor device may include a lower electrode structure having a plurality of lower electrodes vertically stacked on a substrate and an upper electrode structure having a plurality of upper electrodes stacked on the lower electrode structure. Each of the lower and upper electrodes may include an electrode portion that is parallel to a top surface of the substrate and a vertical pad portion that is inclined with respect to the top surface of the substrate. The vertical pad portions of adjacent lower electrodes may be spaced apart from each other by a first horizontal distance. The vertical pad portions of adjacent lower and upper electrodes may be spaced apart from each other by a second horizontal distance that is greater than the first horizontal distance.