Provided is a semiconductor device in which a short margin between a storage contact plug and a bit line contact plug may be increased. The device includes a substrate including isolation regions and active regions defined by the isolation regions, gates disposed in the substrate and configured to intersect the active regions and define source regions and drain regions in the active regions, an interlayer insulating layer disposed on the substrate, bit line contact plugs configured to penetrate the interlayer insulating layer and contact the drain regions, and first bit line structures and second bit line structures disposed on the interlayer insulating layer. The first bit line structures include first bit line conductive patterns and first bit line spacers covering sidewalls of the first bit line conductive patterns. The second bit line structures include second bit line conductive patterns configured to contact the bit line contact plugs to be substantially parallel to the first bit line conductive patterns and first bit line spacers covering sidewalls of the second bit line conductive patterns and sidewalls of the bit line contact plugs.