The effects of a small amount of Ag addition to NiGe ohmic contacts on the electrical properties and the microstructure were investigated. The contact resistance of NiGe contacts was reduced by a factor of about three by adding a 6 nm thick Ag to the NiGe. This contact had a smooth surface, shallow reaction depth, a wide process window, and excellent thermal stability at 300 degrees C after contact formation. The reduction of the contact resistances was believed to be due to for mation of Ag(Ga) solid solutions, which facilitated heavy doping of Ge atoms into the Ga vacancies created at the GaAs surface. The present study suggests that the addition of a third element which has a wide solubility range with Ga is effective for the reduction of the resistances of the NiGe ohmic contacts.