We examined the oxidation behavior at the sidewall of TiSi2/polysilicon gate stack at temperatures of 730-850 degrees C. Oxidation at temperatures above 800 degrees C caused an abnormally enhanced oxidation of the TiSi2 sidewall, which was not observed in unpatterned TiSi2/polysilicon stack. High-resolution transmission electron microscopy showed that a SiO2-TiO2 mixture was produced as a result of the enhanced oxidation of TiSi2 film, indicating that Ti oxidation was dominant during the oxidation. This unexpected result was attributed to the structural aspect, i.e., simultaneous exposure of TiSi2 and polysilicon during oxidation. Our results suggest that the gate reoxidation of TiSi2/polysilicon stack must be performed at temperatures below 750 degrees C.