Epitaxial GaAs layers had been grown by metal organic chemical vapor deposition at 620°C on Ge(100) susbtrates. The surface roughness of the GaAs is greater than that of GaAs bulk wafers and epilayer morphology is influenced by miscut of the Ge substrate. The GaAs/Ge interface is of good quality and devoid of misfit dislocations and antisite defects. However, Ge diffusion into GaAs occurred during epitaxy and resulted in auto-doping. ZrO2 was deposited by magnetron sputtering onto the epi-GaAs. Capacitance voltage measurements show that the TaN/ZrO2/epi-GaAs capacitor has an interfacical with more defects than a ZrO2/bulk GaAs interface. An improved interface with smaller frequency dispersion can be formed by atomic layer deposition of the high-k dielectric layer onto the epi-GaAs.