The diameter and size distribution measurements of nanoparticles on wafers are critical parameters in the semiconductor industry to control transistor quality and increase production rate. A goniometric optical scatter instrument (GOSI) has been developed at the Center for Measurement Standards of the Industrial Technology Research Institute to readily perform polarized light scattering measurements of the diameter and size distribution measurements of nanoparticles on bare and thin film coated wafers. This scatter instrument is capable of distinguishing various types of optical scattering characteristics, which correspond to the diameters of the nanoparticles and thin film thickness, on or near the surfaces by using the Mueller matrix calculation . The experimental results of the GOSI system show good agreement with the theoretical predictions when the GOSI system was employed to measure nanoparticles of diameter 100 nm, 200 nm, and 300 nm on wafers coated with thin films of 2 nm, 5 nm and 10 nm thickness. These results demonstrate that the polarization of light scattered by nanoparticles can be used to determine the size of particulate contaminants on bare and thin film coated silicon wafers.