Homoepitaxial growth of GaAs was studiedin situin an ultrahigh‐vacuum high‐energy electron diffraction (HEED) system. Two surface structures,GaAs(1¯1¯1¯)−(19)1/2andGaAs(1¯1¯1¯)−2, were observed during growth. The transition from one surface structure to the other was found to be a function of the deposition rate and the substrate temperature, with the high‐temperature structure being the(1¯1¯1¯)−(19)1/2. The film growth morphology was studied by the carbon replication technique. Growth by a step mechanism was observed on a bromine‐methanol etched surface while three‐dimensional nuclei were observed on a polished or contaminated surface.