To study the high-field electrical property and the drain current Ion/Ioff ratio of Al2O3/GaSb p-MOSFET, the Poisson and continuity equations with carrier velocity saturation were solved consistently with two-dimensional numerical analysis. The simulation results show that a maximum drain current of 61.2 mA/mm has been reached for 0.75-μm-gate-length GaSb p-MOSFET device. The results have been compared with that of experiment. With change of the channel length and doping-level in substrate GaSb, the drain currents exhibit little change due to the effects of gate capacitance with high-k dielectric and low-threshold voltage. In addition, a high Ion/Ioff ratio with more than three orders of magnitude and relatively low pinch-off leakage current Ioff with 10-15 A/μm are predicted in an ideal condition. The results indicate that GaSb-based MOSFET with high-k dielectric is promising for future p-channel III-V device.