Au-Zn is one of several metal systems applied to p-GaAs to form ohmic contacts. Although it exhibits a fair degree of reliability, the thrust toward higher power and adverse environments raises concern. Observations indicate that the electrical and mechanical properties as well as the stability of AuZn/GaAs vary with Zn thickness. In this study devices with thin and thick layers were tested visually, mechanically and using SEM and X-ray diffraction techniques. Results revealed significantly different reactivity and product chemistry that could significantly affect overall device performance.