The infrared interference measurement has proved to be an accurate and nondestructive means for evaluating the thickness of epitaxially grown films on silicon. The measuring technique is discussed and the necessary relationships are presented. A fringe wavelength vs. film thickness chart is constructed, which enables rapid thickness determination without calculation. The chart is derived for use with silicon films of relatively low carrier concentration deposited on silicon substrates of high carrier concentration (0.007 ohm‐cm‐N‐type). The chart is most useful for low order interference fringes including 12th order. Similar charts are applicable for other semiconductor materials.