Pb/p-Si Schottky barrier diodes (SBDs) with and without thin native oxide layer have been fabricated. The previously polished p-Si wafer has been cleaned by using a traditional RCA clean with the final dip in diluted HF for 30 s. The ohmic contact on the back surface of the wafer was made by evaporation of Aluminium metal and then the wafer was cut into pieces of 5 mm x 5 mm. Other than the sample PbD1, before Schottky contact formation, these pieces with ohmic contact were exposed to clean room air for 1, 5, 10, 15, 30, 45 and 60 days at room temperature to obtain the samples with the native oxide layer on the clean Si surface. The value of the barrier height (BH), Phi(b) first increases with the increasing exposure time to air and then tends to that of the initial sample PbD1. Furthermore, the energy distribution curves of the interface states localized at the native oxide layer-semiconductor interface were determined from the forward bias current-voltage (I-V) characteristics by taking into account the bias dependence of the barrier height. It was seen that the density value of the interface states for the samples with the native oxide layer at all energy positions is lower than that for the initial sample. This is attributed to the passivation of the cleaned Si surface due to the formed native oxide layer. (C) 2002 Published by Elsevier Science B.V.