The frequency (f) and bias voltage (V) dependence of electrical and dielectric properties of Au/SiO2/n-GaAs structures have been investigated in the frequency range of 10 kHz-3 MHz at room temperature by considering the presence of series resistance (R-s). The values of R-s, dielectric constant (epsilon'), dielectric loss (epsilon '') and dielectric loss tangent (tan delta) of these structures were obtained from capacitance-voltage (C-V) and conductance-voltage (G/omega-V) measurements and these parameters were found to be strong functions of frequency and bias voltage. In the forward bias region, C-V plots show a negative capacitance (NC) behavior, hence epsilon'-V plots or each frequency value take negative values as well. Such negative values of C correspond to the maximum of the conductance (G/omega). The crosssection of the C-V plots appears as an abnormality when compared to the conventional behavior of ideal Schottky barrier diode (SBD), metal-insulator-semiconductor (MIS) and metal-oxide-semiconductor (MOS) structures. Such behavior of C and epsilon' has been explained with the minority-carrier injection and relaxation theory. Experimental results show that the dielectric properties of these structures are quite sensitive to frequency and applied bias voltage especially at low frequencies because of continuous density distribution of interface states and their relaxation time. (c) 2011 Elsevier Ltd. All rights reserved.