An inversion-channel electron mobility model for InxGa1-xAs n-channel metal-oxide-semiconductor field-effect transistors (nMOSFETs) with Al2O3 as gate dielectric is established by considering main scattering mechanisms of bulk scattering, Coulomb scattering of interface charges and interface- roughness scattering of the Al2O3/InxGa1-xAs interface. The simulated results are in good agreement with the experimental data. Analyses by using the model indicate that the total electron mobility is mainly limited by the Coulomb scattering of interface charges under weak and medium effective fields and by the interface-roughness scattering under strong effective fields. Therefore, the effective approaches of enhancing the inversion-channel electron mobility are to reduce the interface-state density and roughness of the Al2O3/InxGa1-xAs interface, to properly increase the in content and control the doping concentration of the InxGa1-xAs channel to a suitable value.