In this study we used a low-pressure metal organic vapor phase epitaxy method to investigate the growth of GaAs metal gate semiconductor field effect transistor (MESFET) structures on a Si substrate. The buffer layer between the Si substrate and the grown GaAs epitaxial layers was a composite Ge Si0.05 Ge0.95 Si0.1 Ge0.9 metamorphic layer. We used transmission electron microscopy to observe the microstructures formed in the grown GaAsGe Six Ge1-x Si material and atomic force microscopy to analyze the surface morphology and the formation of antiphase domains in the GaAs epitaxial layers. The measured Hall electron mobility in the channel layer of a MESFET structure grown on a 6° misoriented Si substrate was 2015 cm2 V-1 s-1 with a carrier concentration of 5.0× 1017 cm-3. The MESFET device fabricated on this sample exhibited good current-voltage characteristics.