The intrinsic drain-induced-barrier-lowering (DIBL) characteristics of ultra-thin-body (UTB) MOSFETs with various III-V channel materials (such as GaAs, In0.53Ga0.47As, In0.7Ga0.3As, InAs, In0.2Ga0.8Sb, InSb, etc.) has been investigated and benchmarked with the Si device. Our results indicate that the DIBL of the III-V-on-insulator devices can be worse than what permittivity predicts. The underlying mechanism is proposed. We also show that, with the aid of quantum confinement (along the channel-thickness direction), the DIBL of the III-V devices can be comparable to the Si device.