Low-resistance Ohmic contacts on Al0.3Ga0.7N/GaN high electron mobility transistors (HEMTs) were formed with a Mo/Al/Mo/Au metallization scheme which was annealed at a relatively low temperature of 500 degrees C. A contact resistance of 0.11 +/- 0.05 Omega mm and a specific contact resistivity of 2.63 X 10(-7) Omega cm(2) were achieved. This represents the best low-temperature-annealed Ohmic contacts on GaN-based HEMTs achieved to date. (c) 2006 American Vacuum Society.