We have investigated the feasibility of applying ion beam mixing techniques to the fabrication of Ohmic contacts in GaAs. The approach has been to deposit alternating layers of Au, Ge and Au, Ge, Ni with e-beam evaporation on GaAs and then to irradiate these layers with energetic Si+ ions. Mixing has been studied by employing Rutherford backscattering, Auger electron spectroscopy, and cross-sectional transmission electron microscopy (X-TEM). Differing amounts of mixing have been achieved for Au–Ge layers by using 125 keV Si+ at doses in the range of 1×1015 to 1×1016 cm−2. The kinetics of mixing is greatly reduced in the case of Au–Ge–Ni layers. Ni layers in between Au–Ge layers seem to act as inhibitors for ion beam mixing. It has been observed by X-TEM that a band of dislocation loops is produced in GaAs at a depth of about 600 Å from the interface although computer simulation of range and damage indicate shorter penetration distances. Even at an incident ion energy low enough so that no direct penetration across the interface takes place, dislocation loops are found to be present. Contacts in the presence of a damaged region at the interface showed non-Ohmic behavior. However, selected Au–Ge contacts fabricated with low energy and low dose irradiation showed Ohmic behavior with resistivity ∼10−4 Ω cm2 after annealing at 340 °C for 5 min. Ion beam mixed metallizations showed remarkable improvement in surface morphology after annealing compared to conventionally alloyed contacts.