A semiconductor device and a method of fabricating a semiconductor device, the device including a substrate including an element isolation film and an active region defined by the element isolation film; a word line crossing the active region in a first direction; and a bit line structure on the substrate and connected to the active region, the bit line structure extending in a second direction crossing the first direction, wherein the bit line structure includes a first cell interconnection film including an amorphous material or ruthenium, a second cell interconnection film on and extending along the first cell interconnection film and including ruthenium, and a cell capping film on and extending along the second cell interconnection film.