The effect of rapid thermal annealing on the microstructure and contact resistance of Au/Ni/Au/ Ge/Ni multilayers deposited on InGaAs:Si layers was studied by Auger electron spectroscopy (AES) and the transmission line method. The reaction process at the interfaces after thermal annealing was monitored by Auger depth profiles (AES in conjunction with ion sputtering). We have observed that the formation of a NiGeAs layer at the interface plays an important role in obtaining contacts with low specific resistance, similar to GaAs. Based on these results, we have obtained extremely low specific contact resistance [(4 +/- 1) x 10(-8) Omega cm(2)] for annealing temperatures higher than 400 degrees C.