A semiconductor memory device, and a method of manufacturing the same, includes a lower stack in which a plurality of first interlayer insulating layers and first conductive layers are alternately stacked, a plurality of cell plugs passing through the lower stack in a vertical direction, an upper stack in which a plurality of second interlayer insulating layers and at least one second conductive layer are alternately stacked on the lower stack, a plurality of drain select plugs passing through the upper stack and being in contact with an upper portion of the plurality of cell plugs, and a separation pattern separating adjacent drain select plugs among the plurality of drain select plugs, wherein the separation pattern is in contact with a sidewall of each of the adjacent drain select plugs.