Voids formed in gold-aluminum intermetallic compounds are known to degrade the long-term reliability of gold wire bonds to aluminum pads. We have investigated the diffusion behavior in the bonds annealed at elevated temperatures. The annealing environment has great influence on the voiding as well as the intermetallic formation. The ball bonds to aluminum pads after annealing in gaseous environments (Ar, N2, Ar+3%H2, Ar+500ppmO2 and air) exhibited sizable voids in the gold/compound interface causing the bond failure. However in the case of vacuum annealing the shear strength increases. The compound layer grows uniformly across the entire interface. There are no deleterious voids observed. It is confirmed that high reliability in the gold/aluminum interface can be obtained by vacuum annealing. Effects of the thickness of aluminum pads and bonding conditions on the voiding have been investigated.