Au-catalyzed self-assembly of GaAs nanowires on (1¯1¯1¯)B GaAs by metalorganic vapor phase epitaxy is reported between 375 and 500 °C, using tertiarybutylarsine and trimethylgallium in H2. The nanowires are (1¯1¯1¯)B aligned and kink-free. Below 425 °C the nanowires have narrow base diameter distributions, closely matching the size 60 nm of the Au nanoparticles at their tip no tapering. Above 425 °C the nanowires show a exagonal-based pyramidal shape with base edges normal to the [211] in-plane substrate directions and base diameters which increase exponentially with temperature, indicating a kinetics limited growth along the nanowire sidewalls. Activation energies in the range of 20–23 kcal/mol were estimated for growth along both the sidewalls and the (1¯1¯1¯)B direction.