The put-pose of this paper is to analyze electrical characteristics in Au/SiO2/n-Si (MOS) capacitors by using the high-low frequency (C-HF-C-LF) capacitance and conductance methods. The capacitance-voltage (C-V) and conductance-voltage (G/omega-V) measurements have been carried out in the frequency range of 1 kHz-10 MHz and bias voltage range of (-12 V) to (12 V) at room temperature. It was found that both C and G/omega of the MOS capacitor were quite sensitive to frequency at relatively low frequencies, and decrease with increasing frequency. The increase in capacitance especially at low frequencies is resulting from the presence of interface states at Si/SiO2 interface. Therefore, the interfacial states can more easily follow an ac signal at low frequencies, consequently, which contributes to the improvement of electrical properties of MOS capacitor. The interface states density (N-ss) have been determined by taking into account the surface potential as a function of applied bias. The energy density distribution profile of N-ss was obtained from C-HF-C-LF capacitance method and gives a peak at about the mid-gap of Si. In addition, the high frequency (1 MHz) capacitance and conductance values measured under both reverse and forward bias have been corrected for the effect of series resistance (R-s) to obtain the real capacitance of MOS capacitors. The frequency dependent C-V and G/omega-V characteristics confirm that the N-ss and R-s of the MOS capacitors are important parameters that strongly influence the electrical properties of MOS capacitors. (C) 2008 Elsevier B.V. All rights reserved.