Interface state density of Pt/p-strained-Si Schottky contacts has been determined using experimental forward bias current-voltage (J-V) and capacitance-voltage (C-V techniques. The effects of interfacial oxide layers and series resistance present in the structure have been studied using a SEMICAD device simulator. It is shown that the interface state density can be obtained directly from the measure of C-V data and is found to decrease as the energy from the edge of the valence band increases.