Ultrathin oxides (<5 nm) of silicon have gained tremendous importance in the context of silicon submicron devices. In the present study ultrathin oxides of silicon are grown by wet oxidation (at 800C) at different water vapor pressures in the range 0.04-1.0 atm. Oxide growth rate is studied as a function of water vapor pressure. The ultrathin oxides grown with this approach are characterized by fabricating MOS tunnel diodes and by studying their capacitance-voltage (C-V), current-voltage (I-V) and charge trapping characteristics as well as the breakdown field. It is shown that the ultrathin oxides grown by wet oxidation method at low water vapor pressure have excellent thickness uniformity and high break down field strength.