The Pd/Ge/Au/Ni/Au and Pd/Ge/Pd/Ti/Au ohmic contact systems on n-PnGaAs were investigated and compared. In both contacts, a good ohmic behavior was obtained even without annealing. This is due to their lower barrier height. The contact resistivity was further decreased by rapid thermal annealing. The Pd/Ge/Au/Ni/Au contact was degraded by intermixing of the ohmic metals with InGaAs above 425 degrees C. This indicates that the Ni layer could not act as a diffusion barrier in this contact system. The out-diffusion of the In and As atoms also deteriorated the ohmic contact due to both an increase in barrier height and charge compensation. The Pd/Ge/Pd/Ti/Au contact showed better ohmic behavior compared with the Pd/Ge/Au/Ni/Au contact, especially at high temperature. The Ti layer acted as the diffusion barrier. Non-spiking and planar interfaces were observed even at 450 degrees C.