In order to improve the power efficiency and reliability of GaSb-based semiconductor lasers, the formation mechanism of ohmic contact of GaSb-based semiconductor lasers is investigated and a new four-layer metal structure (Ni/AuGe/Mo/Au) is proposed. Au/Mo/AuGe/Ni/n-GaSb annealed at 150 ℃~450 ℃ is studied. The results show that the new structure has good ohmic contact characteristics with a low contact resistance, which is conducive to improve the power efficiency of the semiconductor lasers. It is revealed that the atom in-diffusion is decreased and the new metallization has a smooth surface morphology by the analysis of Auger electron spectroscopy, which contributes to improve the reliability of GaSb-based semiconductor lasers.