Raman scattering has been used to investigate the optical phonons in thick compositionally uniform epilayers of In1−xAlxSb (x<0.65) grown by magnetron sputter epitaxy on (001)InSb. An analysis of the stress‐induced changes in the frequencies of the two optical phonon modes found in the epilayers was performed, and the stress factors and phonon mode behaviors for bulk material were evaluated. It was found that some epilayers with lowxvalues were coherently strained, even though their thicknesses far exceeded the mechanical‐equilibrium critical thickness limit.