Contact angle measurements between pure water and etched and nonetched p-type single-crystal pieces of silicon under different illumination conditions have been performed by direct measurement and by photographic analysis. The results indicate that the observed contact angles depend on the wavelength of the illumination used, as well as the condition of the sample surface. For the etched surface, violet light gave the largest contact angles and red light the smallest. In the case of the nonetched silicon red light resulted in the largest angles and violet in the smallest. The results are discussed in terms of the photovoltage effect and charge trapping in the oxide layer.