A semiconductor device and a method of forming the same are provided. The semiconductor device including a first conductive line on a substrate, memory cell structures stacked on the first conductive line, a second conductive line between the memory cell structures; and a third conductive line on the memory cell structures may be provided. Each of the plurality of memory cell structures includes a data storage material pattern, a switching material pattern, and a plurality of electrode patterns, at least one of the electrode patterns includes at least one of carbon material layer or a carbon-containing material layer, and the at least one of the electrode patterns includes a first region doped with a nitrogen and a second region that is not doped with the nitrogen, or is doped with the nitrogen at a first concentration lower than a second concentration of the nitrogen in the first region.