The temperature dependence of capacitance-voltage (C-V) and the conductance-voltage (G/w-V) characteristics of (Ni/Au)/Al0.3Ga0.7N/AlN/GaN heterostructures were investigated by considering the effect of series resistance (R-s) and interface states N-ss in a wide temperature range (79-395 K). Our experimental results show that both R-s and N-ss were found to be strongly functional with temperature and bias voltage. Therefore, they affect the (C-V) and (G/w-V) characteristics. The values of capacitance give two peaks at high temperatures, and a crossing at a certain bias voltage point (similar to 3.5 V). The first capacitance peaks are located in the forward bias region (similar to 0.1 V) at a low temperature. However, from 295 K the second capacitance peaks appear and then shift towards the reverse bias region that is located at similar to-4.5 V with increasing temperature. Such behavior, as demonstrated by these anomalous peaks, can be attributed to the thermal restructuring and reordering of the interface states. The capacitance (C.) and conductance (G/w-V) values that were measured under both reverse and forward bias were corrected for the effect of series resistance in order to obtain the real diode capacitance and conductance. The density of N-ss, depending on the temperature, was determined from the (C-V) and (G/w-V) data using the Hill-Coleman Method. (C) 2008 Elsevier B.V. All rights reserved.