Abstract: A new polarization transmittance difference method has been developed to measure inner strains in semiconductor substrate materials.By using polarization modulation technique in this method，the process becomes simple，quick and the re· suits become more correct for there is no need to rotate samples or polarized elements to measure many times like in other methods.Two-dimensional distribution of inner strains in integral materials can be shown.This method is non·destructive.

Key words: polarization transmittance difference, inner strain, photo-elastic effect, PEM