In this study, we demonstrate the growth of a 150-nm-thick GaSb layer on a GaAs substrate with excellent film quality using the interfacial misfit dislocation growth mode by the Metal-Organic Chemical Vapor Deposition technique. The n-type GaSb epilayer grown on the GaAs substrate has a low threading dislocation density of 3.2 × 106 cm-2 and a surface roughness of approximately 0.8 nm. A high carrier mobility up to 4600 cm2 V-1s-1 with a carrier concentration of 1.2 × 1017 cm-3 is achieved in this study. The fabricated Al2O3/GaSb/GaAs MOSCAP demonstrated excellent capacitance-voltage (C-V) characteristics with a small frequency dispersion of approximately 2.8%/decade. The results demonstrate the potential of high-mobility Sb-based materials on GaAs for p-type channel CMOS applications in the future.