An integrated circuit device includes: a substrate having a cell array area, which includes a first active region, and a peripheral circuit area, which includes a second active region; a direct contact connected to the first active region in the cell array area; a bit line structure connected to the direct contact in the cell array area; and a peripheral circuit gate structure on the second active region in the peripheral circuit area, wherein the peripheral circuit gate structure includes two doped semiconductor layers each being doped with a charge carrier impurity having different doping concentrations from each other.