The contribution of energy band deformation to the elasto‐optic coefficients of hexagonal semiconductors is calculated. It is shown that this contribution accounts for the large dispersion previously observed in certain elasto‐optic coefficients near the band edges of CdS and ZnO. The results are also shown to apply, at least qualitatively, to cubic semiconductors. The effect of the bandgap on the Pockels coefficients of hexagonal semiconductors is also treated.