The frequency dependence of admittance measurements (capacitance-voltage (C-V) and conductance-voltage (G/omega-V)) of Au/SnO2/n-Si (MOS) capacitors was investigated by taking into account the effects of the interface states (N-ss) and series resistance (R-s) at room temperature. Admittance measurements were carried out in frequency and bias voltage ranges of 1 kHz-1 MHz and (-5 V)-(+9 V), respectively. The values of Nss and Rs were determined by using a conductance method and estimating from the admittance measurements of the MOS capacitors. At low frequencies, the interface states can follow the AC signal and yield excess capacitance and conductance. In addition, the parallel conductance (G(p)/omega) versus log (f) curves at various voltages include a peak due to the presence of interface states. It is observed that the Nss and their time constant (tau) range from 1.23 x 10(12) eV(-1).cm(2) to 1.47 x 10(12) eV(-1).cm(2) and from 7.29 x 10(-5) s to 1.81 x 10(-5) s, respectively.