Pulsed-resistivity and Hall-effect measurements have been performed at room temperature on n-type GaAs samples, as a function of electric field, up to the threshold for microwave oscillations. High sensitivity was obtained by using a null detection method. The changes in resistivity and Hall mobility are ∼15% at threshold. For intermediate electric fields the dependence is quadratic in field. The Hall-constant exhibits a nonmonotonic over-all increase of less than 2%, tentatively explained by a variation in the scattering factor. The results are then consistent with a distribution function not significantly different from a displaced Maxwellian, in the range of field studied. © 1967 The American Physical Society.