Themagnetoresistanceeffectofap–njunctionunderanelectricfieldwhichisintroducedbythegatevoltageatroomtemperatureisinvestigatedbysimulation.Asauxiliarymodels,theLombardiCVTmodelandcarriergenerationrecombinationmodelareintroducedintoadrift-diffusiontransportmodelandcarriercontinuityequations.Alltheequationsarediscretizedbythefinite-differencemethodandtheboxintegrationmethodandthensolvedbyNewtoniteration.Takingadvantageofthosemodelsandmethods,anabruptjunctionwithuniformdopingisstudiedsystematically,andthemagnetoresistanceasafunctionofdopingconcentration,SiO_2thicknessandgeometricalsizeisalsoinvestigated.Thesimulationresultsshowthatthemagnetoresistance(MR)canbecontrolledsubstantiallybythegateandisdependentonthepolarityofthemagneticfield.