The results of the work quantitatively and qualitatively illuminate the processes of relaxation of misfit stresses arising during the epitaxy of cubic silicon carbide on silicon. Analysis of stress distributions of mechanical stress in 3C-SiC / Si and 3C-SiC / por-Si heterostructures is carried out. The essential role of the porous buffer layer in reducing the magnitude of misfit stresses is shown. The theoretical study data are confirmed by the experimental values of residual stresses in 3C-SiC / Si and 3C-SiC / por-Si samples.