A memory device includes a first cell block on a substrate at a first level, and a second cell block on the substrate at a second level different from the first level. Each of the first and second cell blocks includes a word line extending in a first direction that is parallel to a top surface of the substrate, a word line contact connected to a center point of the word line, a bit line extending in a second direction that is parallel to the top surface of the substrate and intersects the first direction, a bit line contact connected to a center point of the bit line, and a memory cell between the word and bit lines. The second cell block is offset from the first cell block in at least one of the first and second directions.