A semiconductor device includes a substrate including a cell region and a core/peripheral region, a bit line structure disposed on the substrate of the cell region and including a polysilicon structure, a barrier pattern, a metal pattern and a capping pattern that are stacked on each other, and a gate structure on the substrate of the core/peripheral region, the gate structure including a gate insulation pattern, a polysilicon pattern, a carbon-containing pattern, a barrier structure, a metal pattern and a capping pattern that are stacked on each other.