Parasitic capacitance analysis of an ultra thin-film Metal-Semiconductor- Metal(MSM) photodetector(PD) having the lowest capacitance per unit surface area is reported in this paper. Through cladding layers removing process using etching, 50-60% decrease in the parasitic capacitance of the MSM photodetectors, compared to the conventional inverted thin-film MSM photodetectors, was obtained. The parasitic capacitance of the MSM photodetectors depending on etching time was optimized and analyzed using RF modeling techniques in this report. © 2006 IEEE.