The influence of a number of substrate conditions and interfacial contaminants on the adhesion strength of thin Au films (10 to 100 nm thick) to GaAs substrates was studied. The GaAs surfaces were prepared by cleaving on the <110> plane under controlled atmospheres and conditions prior to depositing the Au film. Adhesion strengths were measured using the pinpull test. The study included standard characterization techniques to examine the substrate surface and the Au-GaAs interfaces. A direct correlation was found between cases of poor adhesion and the presence of hydroxyl groups on the GaAs surface. The influence of post evaporative treatments to improve the adhesion of specific cases was also studied.