We report transport measurements on a series of high purity InAs epilayers grown on GaAs substrates by metalorganic chemical vapor deposition using tertiarybutylarsine and trimethylindium. Perfectly specular surfaces were obtained by a two step growth method consisting of a 400 °C prelayer followed by deposition of the thick bulk layer at higher growth temperatures. Temperature dependent Hall measurements between 1.8 and 293 K showed a competition between bulk and surface conduction, with average Hall mobilities of up to 1.2×105cm2/V s at 50 K. Large changes in the temperature dependent transport data are observed several hours after Hall contact formation and appear to be due to passivation of the surface accumulation layer by native oxide formation. ©1995 American Institute of Physics.