We have investigated the processes of Au-In alloy formation in Au/InSb(111)A system by using TED (transmission electron diffraction) and HR-TEM (high-resolution transmission electron microscopy) in the plan-view and profile geometries. At room temperature, the Au9In4 alloy with a γ-brass structure emerges on the InSb(111)A surface with an Au coverage of 3 ML. Subsequent annealing at 150oC leads to the structural and stoichiometric changes from Au9In4 to AuIn2 that fits the substrate better than Au9In4 (0.6% for AuIn2 and 1.3% for Au9In4). Such changes are promoted by In-rich conditions and high mobility of In atoms induced by high temperature annealing.