Si nanobar field effect transistors (Si-NBFETs) have emerged as one of the potential candidates in the present era of nano-structured electronic devices. In the current work, the carrier transport in ballistic Si-NBFETs is modeled by constructing a relevant Hamitonian matrix, where the coupling of source and drain with the channel is incorporated by the corresponding self-energy matrices. The Hamiltonian is solved by non-equilibrium Green's function formalism. The current-voltage characteristics for different width and thickness of the nanobar channel are investigated in detail. Comparative study on drive current and leakage current for various transverse dimensions suggests a cross-sectional design window with an aspect ratio in the range of 1.3-1.6 to be appropriate for superior performance. © 2012 SPIE.