High-resolution electron-energy-loss spectroscopy (HREELS) has been used as a noninvasive probe to investigate the plasmon excitations and accumulation layers and determine the nominal electron mobility in the near-surface region of undoped molecular beam epitaxial-grown InAs(100). HREEL spectra were recorded at 300 and 600 K, over a wide range of incident electron energies, to observe the effects of temperature on the electron mobility, carrier concentration, surface state density, accumulation layer profile, and plasmon damping mechanisms. These data have been analyzed using semiclassical dielectric theory with a three-layer model, using a simple Drude dielectric function. A separate wave-vector-dependent Landau damping term was included to allow momentum scattering to be described independently by the usual phenomenological damping term. The probing electron energy and temperature dependence of this momentum damping is used to gauge the relative contributions of surface scattering, ionized impurity scattering, and phonon scattering. By extracting the surface scattering component of the plasmon damping, bulk mobility values have been estimated and are much higher than those determined from the high probing electron energy plasmon damping parameters. The bulk electron mobilities and bulk carrier concentrations are 28 800 cm(2) v(-1) s(-1) and 2 X 10(16) cm(-3) at 300 K, respectively, and 12 900 cm(2) V-1 s(-1) and 2 X 10(17) cm(-3) at 600 K.