A method of manufacturing a memory device includes sequentially forming and then etching a preliminary selection device layer, a preliminary middle electrode layer, and a preliminary variable resistance layer on a substrate, thereby forming a selection device, a middle electrode, and a variable resistance layer. At least one of a side portion of the selection device or a side portion of the variable resistance layer is removed so that a first width of the middle electrode in a first direction parallel to a top of the substrate is greater than a second width of the variable resistance layer in the first direction or a third width of the selection device in the first direction. A capping layer is formed on at least one of a side wall of the etched side portion of the selection device or a side wall of the etched side portion of the variable resistance layer.