The performance of III-V channel ultra-thin-body Schottky barrier (SB) MOSFETs is assessed by quantum mechanical simulations. All the Gamma-, L-, and Delta-valleys are included in the calculations, with their effective masses adjusted by the sp(3)d(5)s* tight-binding method. Our results show that InSb and InAs channel devices are not adequate for SB devices due to high ambipolar currents. InSb, InAs, and GaAs channel devices suffer from the serious density-of-states (DOS) bottleneck problem. Their transconductances are only about 1/4 of that of Si channel devices. On the other hand, GaSb channel devices which are immune from the DOS bottleneck show excellent performance. The transconductance and ON-state current that are, respectively, 1.2 and 1.8 times as large as that of Si-based devices can be achievable.