Thermal stability of novel Pd/Sn and Pd/Sn/Au Ohmic contacts to n-GaAs has been investigated and compared to the non-alloyed Pd/Ge and alloyed Au-Ge/Ni metallizations. Metallization samples are furnace annealed at various temperatures and systematically characterized utilizing Scanning Electron Microscopy (SEM) and current-voltage (I-V) measurements. Contact resistivities, rho(c), of the proposed metallization are measured using a conventional Transmission Line Model (cTLM) method. The Pd/Sn Ohmic contacts display superior thermal stability at 410 degrees C when compared to the Pd/Ge contacts. After annealing at 410 degrees C for 4 h, rho(c) of the Pd(50 nm)/Sn(125 nm) metallization remains in the low 10(-5) Omega cm(2) range, whereas rho(c) values increase to 10(-4) Omega cm(2) for the Pd(50 nm)/Ge(126 nm) contacts. At 410 degrees C, the Pd/Sn/Au metallizations also display better thermal stability than that of non-alloyed Pd/Ge and alloyed Au-Ge/Ni metallizations. The long-term stability at 300 degrees C of the Pd/Sn and Pd/Sn/Au Ohmic contacts is also reported.