We examine the physics of ballistic transport in a nanoscale MOSFET as reflected in the shape of the distribution function. We calculate the electron distribution function in the ballistic limit by solving the ID steady-state Boltzmann transport equation self-consistently with the 2D Poisson equation in an n-channel ultra-thin-body nanoscale double-gate SOI MOSFET. In equilibrium, symmetry of the distribution function is achieved through balanced carrier injections from the source and drain contacts. Under bias, the distribution function displays distinctive features of ballistic transport- a discontinuous asymmetric shape and the development of a discontinuous ballistic peak. We discuss the implications of ballistic transport to modeling of nanoscale MOSFETs based on moment-based macroscopic transport models. (C) 2002 Elsevier Science Ltd. All rights reserved.