A memory device including first conductive lines spaced apart from each other and extending in a first direction; second conductive lines spaced apart from each other and extending in a second direction that is different from the first direction; first memory cells having a structure that includes a selection device layer, a middle electrode layer, a variable resistance layer, and a top electrode layer; and insulating structures arranged alternately with the first memory cells in the second direction under the second conductive lines, wherein the first insulating structures have a top surface that is higher than a top surface of the first top electrode layer, and the second conductive lines have a structure that includes convex and concave portions, the convex portions being connected to the top surface of the top electrode layer and the concave portions accommodating the insulating structures between the convex portions.