An alloyed PdGeCu Ohmic contact to n -type GaAs is reported for the first time. The PdGeCu Ohmic contact exhibited a very low specific contact resistance of 5.73× 10-7 cm2 at a low annealing temperature of 250 °C. This result is comparable to the reported PdGe and AuGeNi Ohmic contact systems to n -type GaAs with doping concentrations about 1× 1018 cm-3. The Ohmic contact formation mechanisms and microstructure evolution were investigated using secondary ion mass spectrometry, x-ray diffraction, transmission electron microscopy, and energy dispersive spectrometer. The Ohmic contact behavior was related to the formation of Cu3 Ge and Pd Gax Asy compounds after annealing.