A phenomenological expression is derived for the calculation of the spectral dependence of the linear electro-optic coefficients in zinc-blende-type semiconductors. Analyses are presented for GaAs, and results are in good agreement with published experimental data when a lifetime broadening effect is taken into consideration in the model. It is also found that the E0 gap (lowest-direct gap) strongly contributes to the dispersion of the linear electro-optic coefficients, but not to its absolute value.