A model of the basic processes accompanying solid‐phase reactions (SPR) on the Si surface has been developed based on general physical considerations. The model considers these processes in various structures, including M–Si, Si–SiO2, and Si–Si3N4. Analytical expressions have been derived to estimate values of the elastic stresses, steady‐state crystal supersaturation by point defects, and SPR activation energy. Data related to the type of point defect generated during SPR have been obtained. A rule to predict the sequence of phase formation in systems with a polyphase constitution diagram is proposed. In particular it is shown that the steady‐state crystal supersaturation by self‐interstitials during thermal oxidation of Si ranges from 2.4 to 4.4 at 1200 °C. However, the supersaturation by vacancies during the metal silicide formation varies in range from 102to 107depending on the reaction type and temperature. The analytical results have been compared with experimental data on the enhanced diffusion of impurities, growth of oxidation stacking faults, and growth parameters of metal silicide layers, and have shown good agreement. ©1996 American Institute of Physics.