The critical resolved shear stress of GaAs single crystals doped with silicon was directly measured using dynamical compression tests at high temperatures. At the melting point the critical resolved shear stress is 0.032 and 0.027 kg/mm2for crystals doped with 1.5×1018and 3×1018cm−3silicon, respectively. These values are lower than that for undoped GaAs. This reinforces our earlier conclusion that solid solution hardening and the reduction of crystallographic glide is not the only mechanism by which dopants reduce the formation of dislocations during the growth of single crystals from the melt.