Abstract: The phenomenon of self-organized change in the composition of epitaxial layers of the Al_xGa_1 ‒ xN solid solution during their growth by chloride-hydride epitaxy on SiC/Si(111) hybrid substrates is discovered using spectral ellipsometry, Raman spectroscopy, and scanning microscopy with an X-ray spectrometer. It is found that interlayers or domains consisting of AlGaN of stoichiometric composition appear during the growth of Al_xGa_1 – xN layers with a low (about 11–24%) content of Al. A qualitative model is proposed, according to which self-organization in composition occurs due to the effect of two processes on the growth kinetics of the Al_xGa_1 – xN film. The first process is associated with the competition of two chemical reactions proceeding at different rates. One of these reactions is the formation of AlN; the second reaction is the formation of GaN. The second process, closely related to the first one, is the appearance of elastic compressive and tensile stresses during the growth of Al_xGa_1 – xN films on SiC/Si(111). Both processes influence each other, which leads to a complex pattern of aperiodic variation of the composition over the thickness of the film layer.