Owing to the high carrier mobility, two-dimensional (2D) gallium antimonite (GaSb) is a promising channel material for field-effect transistors (FETs) in the post-silicon era. We investigated the ballistic performance of the 2D GaSb metal–oxide–semiconductor FETs with a 10 nm-gate-length by the ab initio quantum transport simulation. Because of the wider bandgap and better gate-control ability, the performance of the 10-nm monolayer (ML) GaSb FETs is generally superior to the bilayer counterparts, including the three-to-four orders of magnitude larger on-current. Via hydrogenation, the delay-time and power consumption can be further enhanced with magnitude up to 35% and 57%, respectively, thanks to the expanded bandgap. The 10-nm ML GaSb FETs can almost meet the International Technology Roadmap for Semiconductors (ITRS) for high-performance demands in terms of the on-state current, intrinsic delay time, and power-delay product.