The electrical and reliability characteristics of ultrathin gate oxide, annealed in ND3 gas, have been investigated. Compared with a control oxide, which had been annealed in NH3, the ND3-nitrided oxide exhibits a significant reduction in charge trapping and interface-state generation. The improvement of electrical and reliability characteristics can be explained by the strong Si–D bond at the Si/SiO2 interface. This nitridation process of a gate dielectric using ND3 has considerable potential for future ultra-large-scale integration device applications. © 2000 American Institute of Physics.