Ultra-thin silicon dioxides were grown on p-type(100) oriented silicon employing rapid thermal dry oxidation technique at the temperature range of 850∼1050 $^{circ}C$. The growth rate of the ultra-thin film was fitted well with tile model which was proposed recently by da Silva ＆ Stosic. The capacitance-voltage, current-voltage, characteristics were used to study the electrical properties of these thin oxides. The minimum interface state density around the midgap of the MOS capacitor having oxide thickness of 111.6 $AA$ derived from the C-V curve was ranged from 6 to 10${ imes}$10$^{10}$ /$ extrm{cm}^2$eV.