We investigated the characteristics of the HfO2 layer deposited by ALD method in MOSFET devices where the HfO2 film is incorporated as the gate dielectric layer. The HfO2 film was annealed with forming gas (FG) or high-pressure D-2 gas to investigate the effect of annealing on the characteristics of the MOSFET device. It was found that the drain current and transconductance of the D-2-annealed MOSFET device increased remarkably by similar to 10% compared with those of FG-annealed MOSFET device, which is a definite improvement that may contribute to reliable operation of the ultra high-density MOSFET devices.