The interface trap density of statesDitof ultrathin SiO2film has been investigated as a function of process variables. The process parameters used were oxidation temperature (1000–1200 °C), oxide thickness (4–10 nm), and annealing condition, including ambient (deuterium, argon, and in vacuum), temperature (500 and 900 °C), and time (10–120 s). Analysis of as‐grown SiO2films showed that theDitdecreases with increasing oxidation temperature and/or oxide thickness. With annealing in argon or in vacuum at 900 °C, theDitdecreases exponentially at the initial stage, then starts to increase linearly with increasing time. Similar behavior was observed for 900 °C deuterium annealing. Deuterium annealing at 500 °C was more effective in the reduction of theDit, whereas argon annealing at the same temperature did not affect the density at all. A possible model for annealing kinetics is proposed to explain the experimental results.