Non-alloyed thermally stable Pd/Sn and Pd/Sn/Au Ohmic contacts have been utilized for the fabrication of GaAs MESFETs for the first time. MESFETs with non-alloyed Pd/Ge Ohmic contacts are also investigated for comparison. All contacts were deposited using a resistance heating evaporator and were furnace annealed in a conventional graphite strip annealer. Contact resistivities, ρ c, of the metallizations were measured utilizing the conventional transmission line model (cTLM) method. Metallization samples were characterized utilizing scanning electron microscopy (SEM) and current–voltage ( I–V) measurements. Morphological characteristics display significant impact on the edge uniformity of the contacts. The maximum amplitude of the undulation with Pd/Sn/Au contacts is ∼100 nm. MESFETs with Pd/Sn/Au metallizations show improved extrinsic transconductance, g m, when compared to the MESFETs with Pd/Sn and Pd/Ge contacts. The calculated g m for the MESFETs with Pd/Sn/Au metallizations is more than 100 mS/mm for a gate length, L G, of 2 μm. Experimental results show that non-alloyed thermally stable Pd/Sn/Au Ohmic contacts appear to be promising candidates for GaAs devices.