The separations of two partials of individual extended dislocations in undoped, Si-doped, Zn-doped and Cr-doped single crystals of GaAs, deformed at 723, 823 or 923K were measured using the weak-beam technique of electron microscopy, and the stacking-fault energy was determined. The average stacking-fault energy determined was 42mJ/m2. No appreciable effects of dopants or deformation temperature upon the stacking-fault energy were observed.