The true and apparent temperature of samples during the deposition of III-V layers by molecular beam epitaxy changes as a result of the variation in spectral emissivityϵ with layer thickness. Taking into account the infrared optical propertiesof these materials, we modelized the variations of the true sample temperature and theapparent temperature (as determined by pyrometric measurement) during the growth. Welimited our study to deposits involving at least one absorbing material (at thepyrometer wavelength), for example GaSb, InAs or InSb. We showed that our simple modelcan agree reasonably with experiments in the 400−500 °C temperature range.