A detailed physical model of pyrometric interferometry during molecular beam epitaxy growth of III–V layers is presented. The pyrometric radiation intensity is expressed as spatial convolution of the spontaneous emission rates and the propagation response of the sample. The new formalism, together with empirical modeling of background signal provide a generic framework for implementing a model‐reference closed‐loop control system for epitaxial growth of multilayer structures. ©1995 American Institute of Physics.