A numerical simulation methodology for incorporating thermo-magnetic effects on the MOSFET gate tunneling current is introduced. The methodology is based on the solution of the Schrödinger-Poisson coupled system, which allows simulating the influence of a static magnetic field and temperature on the wavefunctions and gate tunneling current of MOSFET devices. In addition to the preliminary results on the simulation methodology, experimental results on the effect of the magnetic field on the subthreshold slope, the off-current, and transconductance, are also introduced. The proposed simulation methodology, in conjunction with experimental data, is useful for device degradation and reliability studies in nano-scaled MOSFET devices. This experimental characterization technique sets also the basis for the development of a magnetic force nanoscopy technique, where the conductive properties, thanks to the Lorentz force, can be two-dimensionally mapped over the nano-scaled MOSFET channel plane.