A wiring structure includes a first plug extending through a first insulating interlayer on a substrate, a first wiring extending through a second insulating interlayer on the first insulating interlayer and the first wiring is electrically connected to the first plug, a diffusion barrier layer pattern on the first wiring and on the second insulating interlayer, a portion of the second insulating interlayer being free of being covered by the diffusion barrier layer pattern, a second plug extending through the diffusion barrier layer pattern, the second plug is in contact with the first wiring, and a second wiring electrically connected to the second plug.