The frequency dependence of capacitance-voltage (C-V) and conductance-voltage (G/omega-V) characteristics of the Al/SiO2/p-Si metalinsulator-semiconductor (MIS) structures has been investigated taking into account the effect of the series resistance (R,) and interface states (N-ss) at room temperature. The C-V and G/omega-V measurements have been carried out in the frequency range of 1 kHz to 1 MHz. The frequency dispersion in capacitance and conductance can be interpreted only in terms of interface states and series resistance. The N-ss can follow the ac signal and yield an excess capacitance especially at low frequencies. In low frequencies, the values of measured C and G/omega decrease in depletion and accumulation regions with increasing frequencies due to a continuous density distribution of interface states. The C-V plots exhibit anomalous peaks due to the N-ss and R-s, effect. It has been experimentally determined that the peak positions in the C-V plot shift towards lower voltages and the peak value of the capacitance decreases with increasing frequency. The effect of series resistance on the capacitance is found appreciable at higher frequencies due to the interface state capacitance decreasing with increasing frequency. In addition, the high-frequency capacitance (C-m) and conductance (G(m)/omega) values measured under both reverse and forward bias were corrected for the effect of series resistance to obtain the real diode capacitance. Experimental results show that the locations of N-ss and R-s have a significant effect oil electrical characteristics of MIS structures. (c) 2006 Elsevier B.V. All rights reserved.