Sputtered-deposited ZrO2 gate dielectric on epitaxial-GaAs/Ge substrates have been studied for complementary-metal-oxide-semiconductor (CMOS) applications. The epitaxial-GaAs (epi-GaAs) on Ge susbstrates with AlGaAs interlayer was grown by metal-organic chemical vapor deposition at 650oC. High resolution transmission electron microscopy ((HRTEM) shows that the epilayers are free from arsenic anti-phase defects (APD). From secondary ion mass spectrometry, it was confirmed that the Ge diffusion is completely blocked by the AlGaAs layer and no Ge atoms are able to penetrate into the GaAs layer. The macroscopic surface roughness of epitaxial GaAs is ~5.3nm, whereas over 200x200nm is 0.4 nm, which is comparable with bulk GaAs. Althogh, the epi-GaAs has nano-scale surface features; the conduction-AFM shows electrically homogeneous surface. The electrical and interfacial properties of MOS capacitors with sputtered deposited ZrO2 dielectric on epitaxial-GaAs/Ge and bulk GaAs substrates were investigated. The frequency dispersion and hysteresis voltage for directly deposited ZrO2 on epi-GaAs is higher compared with bulk p-GaAs, however, it is comparable with bulk n-GaAs. The interfacial and electrical properties of ZrO2 on epi-GaAs have shown to exhibit better electrical characteristics after post deposition annealing (PDA) at 400oC. The apparent doping profile of the epitaxial layer is unchanged with PDA temperatures, which suggest the less cross-diffusion of Ge, Ga, and As during device fabrication. The degradation of the gate oxide quality and interface properties are mainly due to the high surface roughness of epitaxial layer and also presence of elemental out diffusion of Ga and As.