The trend of high integration and miniaturization of semiconductor has accelerated the development of gold bonding wire with smaller diameter. For the stable bonding of fine wire, it is important to characterize the wire with various diameters during the bonding process. To investigate this relationship, the experiments were done for the various sizes of wire diameter and FAB. The wire size and the FAB size were chosen for the test from 15 um to 25 um and from 1.4 WD (Wire Diameter) to 2.0 WD, respectively. The results showed that as the size of FAB became smaller, the size deviation of FAB increased and FAB itself was tilted to one side. When FAB was formed at the same parameter, the length of HAZ became shorter for the wire with the high temperature of recrystallization. It is also revealed that the length of HAZ decreased for the smaller size of FAB. This phenomenon is considered to be related to the heat generated during the FAB formation.