The purpose of this paper is to analyze interface states in Al/SiO2/p-Si (MIS) Schottky diodes and determine the effect Of SiO2 surface preparation on the interface state energy distribution. The current-voltage (I-V) characteristics of MIS Schottky diodes were measured at room temperature. From the I-V characteristics of the MIS Schottky diode, ideality factor (n) and barrier height (Phi(B)) values of 1.537 and 0.763 eV, respectively, were obtained from a forward bias I-V plot. In addition, the density of interface states (N-ss) as a function of (E-ss-E-v) was extracted from the forward bias I-V measurements by taking into account both the bias dependence of the effective barrier height (Phi(e)), n and R-s for the MIS Schottky diode. The diode shows non-ideal I-V behaviour with ideality factor greater than unity. In addition, the values of series resistance (R-s) were determined using Cheung's method. The I-V characteristics confirmed that the distribution of N-ss, R-s and interfacial insulator layer are important parameters that influence the electrical characteristics of MIS Schottky diodes. (C) 2007 Elsevier B.V. All rights reserved.