A three-dimensional semiconductor memory device including a first peripheral circuit including different decoder circuits, a first memory on the first peripheral circuit, the first memory including a first stack structure having first electrode layers stacked on one another and first inter-electrode dielectric layers therebetween, a first planarized dielectric layer covering an end of the first stack structure, and a through via that penetrates the end of the first stack structure, the through via electrically connected to one of the decoder circuits, and a second memory on the first memory and including a second stack structure having second electrode layers stacked on one another and second inter-electrode dielectric layers therebetween, a second planarized dielectric layer covering an end of the second stack structure, and a cell contact plug electrically connecting one of the second electrode layers to the through via.