Recently W. Kissinger, M. Weidner, H. J. Osten, and M. Eichler [Appl. Phys. Lett.65, 3356 (1994)] reported ellipsometry and electroreflectance measurements on theE0,E1, andE2critical point energies in strained Si1−yCyalloys grown pseudomorphically on Si (001) using molecular‐beam epitaxy. We present a theory explaining these energies using established deformation‐potential theory and interpret the results and their implications for the band structure of these alloys. ©1995 American Institute of Physics.