We propose a phenomenological method to extend isotropic nonequilibrium distribution functions in semiconductors into field‐induced anisotropic forms. We show that the distribution functions which we derive for the &Ggr; valley of GaAs compare favorably to more precise Monte Carlo simulations. A complete set of transport coefficients for the mancroscopic current continuity and energy flux equations is also derived. These transport coefficients should be helpful to study the range of applicability of various hydrodynamic models in ultrasmall devices.