The energy distribution profile of the interface states (N-ss) and their relaxation time (tau) and capture cross section (sigma(p)) of metal-insulator-semiconductor (Al/SiO2/p-Si) Schottky diodes have been investigated by using the high-low frequency capacitance and conductance methods. The capacitance-voltage (C-V) and conductance-voltage (G/w-V) characteristics of these devices were investigated by considering series resistance (R-s) effects in a wide frequency range (5 kHz-1 MHz.). It is shown that the capacitance of the Al/SiO2/p-Si Schottky diode decreases with increasing frequency. The increase in capacitance especially at low frequencies results form the presence of interface states at Si/SiO2 interface. The energy distributions of the interface states and their relaxation time have been determined in the energy range of (0.362-E-v)-(0.512-E-v) eV by taking into account the surface potential as a function of applied bias obtained from the measurable C-V curve (500 Hz) at the lowest frequency. The values of the interface state density (N-ss) ranges from 2.34 x 10(12) to 2.91 x 10(12) eV(-1)/cm(2), and the relaxation time (tau) ranges from 1.05 x 10(-6) to 1.58 x 10(-4) s, Showing all exponential rise with bias from the top of the valance band towards the mid-gap. (C) 2008 Elsevier B.V. All rights reserved.