In order to interpret the effect of illumination on the electrical characteristics of Au/n-CdTe Schottky barrier diodes (SBDs) the forward and reverse bias current-voltage (I-V), capacitance-voltage (C-V), and conductance-voltage (G/w-V) characteristics of these SBDs have been investigated at room temperature using a tungsten lamp under both different illumination levels and in dark. Under illumination, both of the values of forward and reverse currents have increased with increasing illumination intensity. In the reverse bias, the change in current is higher than the forward bias at the same applied bias voltage. This behavior can be attributed that electron-hole pairs generate in the junction as a result of the light absorption. Experimental results show that both of the values of the capacitance and conductance have increased with increasing illumination levels and give the peaks at high illumination levels. The illumination process causes shifts in the capacitance-voltage (C-V) and conductance-voltage (G/w-V) curves towards forward bias and the shifts have increased with increasing illumination level. This behavior can be explained by the built-up of fixed charge between metal and semiconductor which is attributed to the changes in the number of interface states (N-ss) due to the illumination process. In addition, the series resistance (R-s) of diodes can significantly alter the C-V and G/w-V characteristics and decrease with increasing illumination level.