Ohmic contacts between Au and sulfur‐passivatedn‐GaAs have been formed without annealing after deposition of the metal. The GaAs samples doped with either 2×1016or 3×1018cm−3Si were passivated with (NH4)2S in an aqueous solution, then the passivating sulfur was thermally desorbed in a vacuum. Desorption was followed immediately byinsituthermal evaporation of Au with the substrate at room temperature. OhmicI‐Vbehavior was measuredexsitu.C‐Vmeasurements on a sample with a native oxide surface barrier layer showed the surface carrier concentration on the higher doped sample increased from 3×1018to 7×1018cm−3after S desorption. Secondary ion mass spectroscopy data showed that S had diffused into the GaAs surface region. Thus S passivation prevented interfacial oxide formation during the exposure to air after the sample was passivated and before the vacuum chamber was pumped to a low pressure. Sulfur apparently diffused into the surface region during flash desorption in vacuum and increased the surfacen‐doping concentration which led to ohmic contacts without post‐annealing of the Au films.