Dissipative quantum transport simulations using the Non-Equilibrium Green Function Formalism have been carried out to obtain a transfer characteristic of a Si gate-all-around (GAA) nanowire transistor. A donor-type impurity has been located close to the source/channel interface, creating a resonant level. The existence and energy of the resonant level depends on the value of the gate bias. The dependence of the current reduction due to phonon scattering as a function of the gate bias, has a minimum due to the resonant level. The simulations at different temperatures have shown a decline in the sub-threshold slope at high temperature and an improvement at low temperature. Finally, the sub-threshold slope approximate follows the standard linear temperature dependence.