Abstract The charge carrier transport coefficients of InAs epilayers, grown on semi-insulating GaAs by chemical vapor phase heteroepitaxy, were investigated by means of gate-voltage-controlled electrical and galvanomagnetic measurements made on metal-oxide-semiconductor structures. The capacitance versus gate voltage dependence of such structures indicates that in the extrinsic temperature region the epilayer surfaces are accumulated for Vg = 0 and flat-band conditions apply for Vg ≈−31 V. It is shown that if the epilayer thickness is corrected for depletion then the epilayer Hall coefficients and conductivities are independent of Vg and have bulk-like values and that the electron mobility has its bulk-like value and is independent of Vg in depletion. In accumulation, the epilayer properties are considered in terms of a composite two-layer model: a bulk-like region of thickness db with an average flat-band electron density nb = 2.5 × 1015 cm−3 and mobility μb = 7.5 × 104 cm2 V−1 s−1 and a surface-like region of thickness ds with a gate-voltage-dependent surface charge density nsds and mobility μs where nsds (+30 V) = 2.06 × 1012 cm−2 and μs(+30 V) = 1.47 × 104 cm2 V−1 s−1. The monotonic decrease in μs with Vg is attributed to scattering of the conduction electrons by localized surface charges which decrease the specularity of the epilayer surfaces.