The effects of in-situ and ex-situ surface treatments on the electrical properties of GaSb metal-oxide-semiconductor capacitors (MOSCAPs) are compared and investigated. The in-situ approach can provide a native oxide-free GaSb surface subsequent high-κ dielectric deposition. HfO2/Al2O3/p-GaSb MOSCAPs fabricated on an Sb-stabilized surface exhibit clear inversion at low frequency and good modulation of the Fermi level across the whole GaSb band gap. The interfacial trap density (Dit) extracted by the conductance method is about 7.6×1011 cm-2eV-1 near the valence band. As to the ex-situ process, the air-exposed GaSb samples are treated by hydrogen plasma at room temperature prior to dielectric deposition. The capacitance-voltage (C-V) characteristics and gate leakage currents are comparable to those of the MOSCAPs prepared by in-situ method. Dit near the valence as low as 6.0×1011 cm-2eV-1is obtained, indicating the feasibility of using GaSb p-channel MOSFETs for future complementary MOS integrated circuits.