By taking into account simultaneously the effects of border traps and interface states, the authors model the alternating current capacitance-voltage (C-V) behavior of high-mobility substrate metal-oxide-semiconductor (MOS) capacitors. The results are validated with the experimental In_0.53Ga_0.47As/ high-κ and InP/high-κ (C-V) curves. The simulated C-V and conductance-voltage (G-V) curves reproduce comprehensively the experimentally measured capacitance and conductance data as a function of bias voltage and measurement frequency, over the full bias range going from accumulation to inversion and full frequency spectra from 100 Hz to 1 MHz. The interface state densities of In_0.53Ga_0.47As and InP MOS devices with various high-κ dielectrics, together with the corresponding border trap density inside the high-κ oxide, were derived accordingly. The derived interface state densities are consistent to those previously obtained with other measurement methods. The border traps, distributed over the thickness of the high- κ oxide, show a large peak density above the two semiconductor conduction band minima. The total density of border traps extracted is on the order of 10¹⁹ cm^-3. Interface and border trap distributions for InP and In_0.53Ga_0.47As interfaces with high-κ oxides show remarkable similarities on an energy scale relative to the vacuum reference.