We describe the fabrication of III–V metal-oxide-semiconductor (MOS) devices on Ge/Si virtual substrates using molecular-beam epitaxy. Migration-enhanced epitaxy and low temperature normal GaAs growth produced a sufficiently smooth surface to deposit gate oxides. A 300 nm thick GaAs buffer layer was grown, followed by a 10 nm growth of In0.2Ga0.8As high mobility channel layer. An 8.5 nm thick Al2O3 layer was deposited ex situ by atomic-layer deposition. Capacitance-voltage (C-V) characteristics show the unpinning of Fermi level. This work suggests this materials combination as a promising candidate for the design of advanced, nonclassical complementary MOS and optoelectronic devices on Si substrates.