The effects of channel scaling in silicon (Si) and Si-alternative germanium (Ge) and In _0.53 Ga _0.47 As (InGaAs) n-channel devices toward the end of the CMOS roadmap are addressed theoretically. The devices are simulated using a quantum-corrected semiclassical Monte Carlo method. The results are discussed with an emphasis on the underlying physics. Multiple effects of quantum confinement within the channel, far-from equilibrium-degenerate statistics, saddle/slot contact geometries with appropriate material-dependent specific contact resistivities, and appropriate material-dependent source and drain doping concentrations are considered, with the exception of the contact resistivity of Ge, which is idealized to reflect what may be possible if the currently prohibitive contact challenge can be overcome.