Results of C-V and IR studies on Si-SiO//2 systems of thin oxides thermally grown on Czochralski (CZ) and float zone (FZ) wafers are reported. The oxides were grown at 900 degree C in dry oxygen as well as in TCE ambient to get approximately equals 500 angstrom thick SiO//2. The oxide thickness was accurately measured by ellipsometer and capacitance methods. IR absorption spectra revealed the peaks for Si-O and O-Si-O stretching bonds at 830 cm** minus **1 and 1090 cm** minus **1 respectively. An extra peak at 1250 cm** minus **1 was also observed, indicating the presence of SiCH//3 which was used for fixing the sample. The variation of interface state density N//i//t with energy showed an oscillatory behavior at the mid-gap in dry oxide samples along with an increase at the band edges, whereas in TCE oxide samples a smoother variation in N//i//t was noted.