A three-dimensional semiconductor memory device includes a stack on a substrate including electrodes vertically stacked on a substrate, lower insulating patterns disposed between the stack and the substrate, the lower insulating patterns being adjacent to both sidewalls of the stack and being spaced apart from each other, a plurality of vertical structures penetrating the stack and being connected to the substrate, and a data storing pattern between the stack and the vertical structures, the data storing pattern including a portion disposed between the lowermost one of the electrodes and the substrate.