The electrical and dielectric properties of Al/SiO2/p-Si (MOS) structures were studied in the frequency range 10 kHz-10 MHz and in the temperature range 295-400 K. The interfacial oxide layer thickness of 320 A between metal and semiconductor was calculated from the measurement of the oxide capacitance in the strong accumulation region. The frequency and temperature dependence of dielectric constant (epsilon'), dielectric loss (epsilon"), dielectric loss tangent (tan delta) and the ac electrical conductivity (sigma(ac)) are studied for Al/SiO2/p-Si (MOS) structure. The electrical and dielectric properties of MOS structure were calculated from C-V and G-V measurements. Experimental results show that the epsilon' and epsilon" are found to decrease with increasing frequency while sigma(ac) is increased, and epsilon', epsilon", tan delta and sigma(ac) increase with increasing temperature. The values of epsilon', epsilon" and tan delta at 100 kHz were found to be 2.76, 0.17 and 0.06, respectively. The interfacial polarization can be more easily occurred at low frequencies, and the number of interface state density between Si/SiO2 interface, consequently, contributes to the improvement of dielectric properties of Al/SiO2/p-Si (MOS) structure. Also, the effects of interface state density (N-ss) and series resistance (R-s) of the sample on C-V characteristics are investigated. It was found that both capacitance C and conductance G were quite sensitive to temperature and frequency at relatively high temperatures and low frequencies, and the N-ss and R-s decreased with increasing temperature. This is behavior attributed to the thermal restructuring and reordering of the interface. The C-V and G/omega-V characteristics confirmed that the N-ss, R-s and thickness of insulator layer (delta) are important parameters that strongly influence both the electrical and dielectric parameters and conductivity in MOS structures. (c) 2005 Published by Elsevier B.V.