The absolute position of the valence band maxima of the semiconducting InxGa1-xAs alloys relative to the vacuum level, a composition-independent energy level, defined as the Fermi level stabilization energy, E-FS, located similar to4.95 eV below the vacuum level, and the energy interval between the composition dependent conduction band minima or valence band maxima determine the equilibrium surface barriers and band offsets of these alloys and their heterostructures. Charged, amphoteric defects, located on EFS, compensate deliberately introduced donor or acceptor impurities and determine the maximum achievable electron or hole concentrations. Experimental measurements made on undoped or on donor-doped metal-semiconductor and on metal-insulator-semiconductor structures of these alloys, indicate that the composition dependence of the equilibrium surface potentials and metal semiconductor barrier heights are consistent with this vacuum pinning rule. (C) 2003 American Vacuum Society.