A semiconductor device is provided. The semiconductor device includes a substrate including an element isolation layer, the element isolation layer defining an active region, a plurality of word lines traversing the active region in a first direction, and a plurality of bit line structures on the substrate and connected to the active region, the plurality of bit line structures extending in a second direction different from the first direction. Each of the plurality of bit line structures includes a ruthenium line wiring including a bottom surface and a top surface opposite to the bottom surface, a lower graphene layer in contact with the bottom surface of the ruthenium line wiring and extending along the bottom surface of the ruthenium line wiring, and a wiring line capping layer extending along the top surface of the ruthenium line wiring.