A method is disclosed for evaluation of the transition region of a silicon epitaxial wafer comprising obtaining the waveform of an interferogram signal for reflected light by irradiation the silicon epitaxial wafer with infrared radiation followed by measurement of the intensity of the light of the interference fringe employing a Michelson interferometer and obtaining the extent of the transition region of the silicon epitaxial wafer by measuring the distance between the maximum peak of the waveform in the side burst region in the interferogram signal and the peak adjacent to said maximum peak of the waveform in the side burst region in the interferogram signal and the distance between the maximum peak and the bottom first coming after said maximum peak of the waveform in the side burst region in the interferogram signal, or the difference in height between the maximum peak and the bottom first coming after said maximum peak of the waveform in the side burst region in the interferogram signal.