Microdefects in the InSb wafer surface which appear as saucer pits by a preferential etching are observed and counted before or after diffusion bymeans ofmicroscope. The result shows that some of the defects are native to the startingmaterial. some of the defects are induced by diffusion. It is found that the reason induced the defects by diffusion is contamination in the InSb wafer surface. It is showed that the defects induced by diffusion are supp ressed in the. clean InSb wafer surface.