The complex dielectric permittivity (epsilon* = epsilon' - j epsilon '') and ac conductivity (sigma(ac)) of Au/SnO2/n-Si (MOS) structures are studied using capacitance (C) and conductance (G(omega)) measurements in a wide temperature range of 125-400 K for six different frequency values. It is observed that the C and G(omega) values decrease with the increasing frequency, while they increase with the increasing temperature. The observed nature of the C is due to the inability of the dipoles to orient in a rapidly varying electric field. The experimental values of the dielectric constant epsilon', dielectric loss epsilon'', loss tangent tan delta and sigma(ac) are found to be strong functions of frequency and temperature. The values of the epsilon' and epsilon '' are found to decrease with the increasing frequency and increase with the increasing temperature. The sigma(ac) is found to increase with the increasing frequency and temperature. Activation energy (E-a), from the Arrhenius plot, is studied to discuss the conduction mechanism in a MOS structure.