Thermally stable, low-resistance ohmic contacts to GaAs (Si-doped,n=1.6–1.8×1018cm−3) were formed using PdIn metallization sputter-deposited from an alloy target. Average specific contact resistances (&rgr;c) in the 10−6&OHgr; cm2range were reached upon annealing at 600 °C or higher. Contacts annealed under the optimum condition of 850 °C for 15 s exhibited an average&rgr;cof 2.5×10−6&OHgr; cm2. The 100 h of thermal aging at 400 or 500 °C increased their average&rgr;cto 3.0×10−6and 1.0×10−5&OHgr; cm2, respectively. The ohmic behavior of the annealed contacts was ascribed to the exchange of In and Ga atoms between the metallization and the semiconductor and the concomitant formation of InxGa1−xAs, whose presence at the contact interface was confirmed using cross-sectional transmission electron microscopy. ©1997 American Institute of Physics.