This paper describes voids in a gold line, which is a new failure mechanisms of GaAs IC using gold line as interconnection. We have found voids in both first and second metal under DC bias test, current density of 0.67 to 1.27 106 A/cm2 in high temperature range of 230 °C to 260 °C. We have observed carefully the movement of voids during the test and found that voids moved toward a cathode, in the opposite direction of electron flow. The velocity of voids increased with the current density almost proportionally. The moving mechanisms of a void can be explained by assuming that gold atoms move toward an anode by electromigration. The activation energy of the void velocity was 0.84 eV at the cathode side. This was nearly equal to 0.6 eV - 0.9 eV reported on the velocity of the gold island on molybdenum surfaces . The GaAs IC failed at the almost same time as the voids appeared. The activation energy of mean time to failure of the IC was 0.89 eV, which was nearly equal to that of the void velocity at the cathode edge of 0.84 eV.