Comparative thin film adhesion studies were performed on GaAs substrates using Au or Au-Ni-Ge, metallization materials. The influence of parameters such as crystal orientation, substrate surface preparation, deposition vacuum conditions, thickness and composition of films, and post-evaporative treatment such as ion-beam mixing and thermal annealing, on film adhesion was considered. The quality of the adhesion bond was measured using Scotch tape tests and a Sebastian adhesion tester. Film interfaces were characterized using AES, XPS, and RBS techniques. The results indicate that the most important factors dominating the quality of adhesion were surface preparation and the deposition vacuum conditions. Films deposited under optimum conditions were found to adhere so well that the GaAs crystal would fracture before the film would pull free of the substrate. The influence of ion beam mixing on the quality of adhesion was tested and only in the cases of depositions under the less optimum conditions, where the adhesion was poor, could an improvement be made in the adhesive properties.