A three-dimensional semiconductor memory device includes a substrate including a cell array region and a connection region and an electrode structure including first and second electrodes alternatingly and vertically stacked on the substrate and having a stair-step structure on the connection region. Each of the first and second electrodes may include electrode portions provided on the cell array region to extend in a first direction and to be spaced apart from each other in a second direction perpendicular to the first direction, an electrode connecting portion provided on the connection region to extend in the second direction and to horizontally connect the electrode portions to each other, and protrusions provided on the connection region to extend from the electrode connecting portion in the first direction and to be spaced apart from each other in the second direction.