The longitudinal wave-vector-dependent dielectric function ∊(q-->) is calculated for Si, Ge, GaAs, and ZnSe. The energy eigenvalues and wave functions which are used have been obtained from energy-band calculations based on the empirical pseudopotential method. Explicit results are given in the [1, 0, 0], [1, 1, 0], and [1, 1, 1] directions in the range 0<=q<=(4πa). A comparison is made between the present results and the results of other calculations. Some comparisons with experiment are also made.