We have fabricated a thermally stable low-contact-resistance Ni/AuGe/Au contact metal for InP-based high electron mobility transistors (HEMTs) without a heavily doped cap layer. The contact resistance is strongly influenced by the amount of Ni. Minimum contact resistance of 0.19 Omega mm was obtained from a Ni (1 nm)/AuGe (50 nm)/Au (99 nm) contact annealed at 300degreesC for 5 min in N-2. A smooth surface was obtained after contact formation and excellent thermal stability was achieved during isothermal annealing at 350degreesC for 1 h in a N2 ambient. This alloyed ohmic contact satisfies the requirements for device fabrication process steps after the ohmic contact formation. It prevents hole accumulation by eliminating the hole barrier at the carrier-supply layer/ channel interface. It also suppresses the kink phenomena and drain conductance frequency dispersion of InP-based HEMTs, and therefore will greatly facilitate the fabrication of ultrahigh-speed integrated circuits. (C) 2003American Vacuum Society. [DOI: 10.1116/1.1563251].