The characteristics and reliability of the nitrided oxide gate n- and p-MOSFETs with less than 1 atom% nitrogen concentration gate films were investigated in detail. These very light nitridations were accomplished using NH3 gas at low temperatures from 800 degrees C to 900 degrees C. The low nitrogen concentrations, such as 0.13 atom% were obtained by SIMS and AES (Auger electron spectroscopy) measurements. The optimum nitrogen concentration region for the deep-sub-micron device is discussed. It was shown that, with the 0.5 atom% nitrogen concentration, good drivability and good hot carrier reliability were attained at the same time, and they were equivalent to those of the oxynitride gate MOSFETs using N2O gas. The suppression of boron penetration is also discussed.