Extremely low resistance nonalloyed Ti/Pt/Au contacts have been formed to n-InGaAs, p-InGaAs, and n-InAs/InGaAs layers with doping concentrations ranging from 1 to 5×1019 cm−3 for n-type and from 2 to 1×1020 cm−3 for p-type material. The comparative studies reveal specific contact resistances as low as 1.7×10−8 Ω cm2 for the n-InAs/InGaAs system, while the best values obtained for n-InGaAs and p-InGaAs are 4.3 and 4.8×10−8 Ω cm2, respectively. The electrical behavior of the contacts is discussed in relation to the effect of ion beam cleaning and post-deposition annealing. The use of low energy (60 eV) Ar+ bombardment provides atomically clean, contamination free surfaces. Very rapid thermal processing at 400 °C for 1 s was successfully employed in order to restore the original properties of the subsurface layer disordered during ion bombardment. This fabrication sequence ensures formation of intimate contacts without interfacial films and carrier compensation effects. The variation of the specific contact resistance with the reciprocal square root of the carrier concentration indicates that tunneling is the dominant mechanism of current flow through the metal-semiconductor junction. The tunneling origin of the contact characteristics has also been elucidated from the temperature dependence of the contact resistance.