Pyrometric interferometry has been observed during gas-source molecular beam epitaxy (GSMBE) of 3C-SiC on Si substrate using monomethyl silane. The period of the "temperature oscillation'' is shown to correspond to lambda/2n, with the lambda and n being the wavelength used in the monochromatic optical pyrometry and the refractive index of the grown film, respectively. As is the case for other heteroepitaxies, pyrometric interferometry may provide a feasible real-time monitoring method for the growth of 3C-SiC film on Si substrates. (C) 2008 Elsevier B.V. All rights reserved.