Submonolayer coverages of Au on GaAs(001) substrates prepared by variousexsituchemical cleaning procedures using low‐energy ion scattering techniques are investigated. This research is compared with previous results for 1 ML of Au deposited on Si(111). A comparison of the energy spectra showed substantial broadening in the Li+backscattering ion peak from Au deposited on GaAs, as compared to the Au on Si. Li+impact collision ion scattering spectroscopy (ICISS) results showed that the gold formed an ordered overlayer above the Si surface, which was thermally stable to 500 °C. Even for depositions on room‐temperature GaAs(001), shadowing of Au by substrate atoms at low scattering angles showed that Au penetrated below the GaAs surface. The estimate of the average penetration depth into the room‐temperature substrate is two to three atomic planes of the GaAs crystal. An ICISS experiment showed that the Au atoms sampled by the ion beam were not ordered on lattice sites, but appeared to occupy multiple and/or random positions within the substrate. Upon annealing to 300 °C, the gold atoms were more ordered, but did not penetrate significantly further into the GaAs. At higher annealing temperatures, the Au either diffused further into the substrate or became incorporated in islands, and occupied favored subsurface sites.