A novel Ohmic contact system comprising of Pd/Sn metallizations has been developed for n-GaAs and systematically characterized using Scanning Tunneling Microscopy (STM), Scanning Electron Microscopy (SEM), Surface Profilometry measurements, Secondary Ion Mass Spectrometry (SIMS), Energy Dispersive Analysis of X-rays (EDAX) and current-voltage (I-V) measurements. Contact resistivities, pc, of the proposed metallizations are measured utilizing a conventional Transmission Line Model (cTLM) method. The Pd/Sn metallizations show lowest pc 5 2 18 3 in the range of low 10' Q-cm on Si-doped (2x10 cm ') n-GaAs. A Au overlayer improves the characteristics of the Pd/Sn Ohmic contacts. The Pd/Sn/Au contacts 6 2 display lowest pc in the range of low 10' Q-cm . The Pd/Sn and Pd/Sn/Au Ohmic contacts are very adhesive to the substrates. Both Pd/Sn and Pd/Sn/Au contacts exhibit improved characteristics when compared with alloyed Au/Ge/Au/Ni/Au contacts. The Pd/Sn and Pd/Sn/Au metallizations show better thermal stability at 410 °C than non-alloyed Pd/Ge contacts. The Pd/Sn/Au metallizations also display better thermal stability than alloyed eutectic Au-Ge/Ni and Ni/Au-Ge/Ni contacts. However, at this temperature thermal stability of the Pd/Sn/Au metallizations is comparable to that of alloyed Au/Ge/Au/Ni/Au contacts. Long-term stability of the Pd/Sn/Au metallizations at 300 °C is comparable to non-alloyed Pd/Ge contacts. No change in surface morphology is observed after having been annealed at 300 °C for 400 h. At 300 °C, the Pd/Sn/Au metallization exhibits pc which is slightly higher than those of the alloyed Au-Ge/Ni, Ni/Au-Ge/Ni and Au/Ge/Au/Ni/Au contacts. GaAs Metal Semiconductor Field-Effect Transistors (GaAs MESFETs) have been fabricated using Pd/Sn and Pd/Sn/Au metallizations as source/drain contacts. MESFETs fabricated with Pd/Sn/Au Ohmic contacts display improved characteristics when compared to Pd/Sn contacts. MESFETs fabricated with Pd/Sn/Au contacts show comparable edge uniformity to non-alloyed Pd/Ge metallizations which is very important for VLSI GaAs devices. The newly developed, thermally stable, Pd/Sn and Pd/Sn/Au metallizations appear to be promising candidates for future GaAs device technology.