This letter presents a new analytical model of the backscattering coefficient with a unique formulation from low- to high-field conditions and only depending on the form of scattering probabilities. The theoretical development is based on the flux theory and a new definition of scattering probabilities. In this model, the mean free path is given by Monte Carlo simulations. This new expression is further used to investigate the effect of high-field conditions in the quasi-ballistic drain current of the double-gate MOSFET.