The growth of ultrathin oxides of silicon (<5 nm) under low thermal budgets is extremely important in the context of ultralarge scale integration. One of the important factors that influence the growth and quality of the ultrathin oxide is the surface preparation of silicon prior to oxidation. In the present paper, the surface of p-type silicon (with (100) orientation) is prepared by three methods: (i) normal cleaning, (ii) chemical polishing and (iii) sacrificial oxide growth. The ultrathin oxide (in the range 2.0 to 2.5 nm) is grown by a low temperature (600 °C), wet oxidation (0.3 atm of water vapour pressure) technique. These ultrathin oxides are characterized for their electrical properties by fabricating aluminum-thin SiO2-Si tunnel diodes employing conventional current-voltage (I-V) and capacitance-voltage (C-V) techniques. The results indicate that the ultrathin oxides grown on the samples prepared by the `sacrificial oxide growth' method give better oxide quality and uniformity; these results may be supported from the information in the literature that the sacrificial oxide reduces the roughness of the silicon surface.