In this study, the forward and reverse bias current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G/w-V) characteristics of Al-TiW-Pd2Si/n-Si structures were measured at room temperature. In order to see the illumination effect on main structure parameters such as zero-bias-barrier height (Phi(Bo)), ideality factor (n), series resistance (R-s) of structure and interface states (N-ss), the forward and reverse bias I-V, C-V and G/w-V characteristics of Al-TiW-Pd2Si/n-Si structures were investigated in the dark and under various levels of illumination. These main electrical parameters were obtained as function of illumination levels from these measurements. Experimental results show that both the C and G values increase with increasing illumination level due to the illumination-induced interface states. Also, the value of R-s decreases with increasing illumination level. The N-ss profile was obtained for both forward bias I-V characteristics by taking into account the bias dependent of the ideality factor and effective barrier height (Phi(e)) and low-high frequency method. Copyright (C) 2010 John Wiley & Sons, Ltd.