The rates at which hot electrons scatter from the valley to the L and X valleys in GaAs have been measured as a function of electron energy. Scattering times are determined from the relative efficiency of recombination of hot electrons with neutral acceptors at low injected-carrier densities. Representative scattering times are L=540±120 fsec for 0.48-eV electrons and X=180±40 fsec for 0.58-eV electrons. Our results enable us to reconcile the large range of scattering rates reported in other experiments and demonstrate the power of this cw probe to study subpicosecond electron dynamics. © 1989 The American Physical Society.