The effect of pre-oxidation cleaning of silicon surface on the characteristics of Al-thin SiO2-Si tunnel diodes with thin SiO2 (<3 nm) grown by low temperature and low pressure wet oxidation has been reported. The surface of silicon single crystal wafer has been prepared employing three cleaning methods: i) Normal cleaning, ii) Chemical polishing and iii) Stripping of thick oxide. Wet oxidation has been carried out at a temperature of 600 °C, 0.30 atmosphere partial pressure of water vapour for 30 minutes. Al-thin SiO2-Si diodes have been fabricated and the electrical characteristics of these diodes have been studied in detail. The results indicate that the ultrathin oxides grown by `Stripping of thick oxide' method gives more uniformity of the grown oxide.