A heterostructure field effect transistor, HFET, comprising: a gate electrode; a source and a drain; a channel semiconductor comprising GaN and electrically coupling the source and drain with a two dimensional electron gas, 2DEG, coupled to the gate electrode through a gate dielectric material; and a plurality of group III-nitride, III-N, polarization materials located between the channel semiconductor on one side and the source, the drain and the gate dielectric material on the opposite side, spaced apart from the channel semiconductor by a III-N spacer and also coupled to the gate electrode through the gate dielectric material, wherein the plurality of III-N polarization materials further comprises, in a region between the gate dielectric material and the III-N spacer: a first III-N material having a first polarization field with a first polarity that places negative charge at a Ga-polar interface of the channel semiconductor in the absence of an externally applied field from the gate electrode; and a second III-N material having a second polarization field with a second polarity that is opposite the first polarity and is of a magnitude equal to the first polarization field, wherein the first III-N material and the second III-N material materials occupy adjacent lateral regions or islands interfacing the III-N spacer and the gate dielectric. a gate electrode; a source and a drain; a channel semiconductor comprising GaN and electrically coupling the source and drain with a two dimensional electron gas, 2DEG, coupled to the gate electrode through a gate dielectric material; and a plurality of group III-nitride, III-N, polarization materials located between the channel semiconductor on one side and the source, the drain and the gate dielectric material on the opposite side, spaced apart from the channel semiconductor by a III-N spacer and also coupled to the gate electrode through the gate dielectric material, wherein the plurality of III-N polarization materials further comprises, in a region between the gate dielectric material and the III-N spacer: a first III-N material having a first polarization field with a first polarity that places negative charge at a Ga-polar interface of the channel semiconductor in the absence of an externally applied field from the gate electrode; and a second III-N material having a second polarization field with a second polarity that is opposite the first polarity and is of a magnitude equal to the first polarization field, wherein the first III-N material and the second III-N material materials occupy adjacent lateral regions or islands interfacing the III-N spacer and the gate dielectric. a first III-N material having a first polarization field with a first polarity that places negative charge at a Ga-polar interface of the channel semiconductor in the absence of an externally applied field from the gate electrode; and a second III-N material having a second polarization field with a second polarity that is opposite the first polarity and is of a magnitude equal to the first polarization field, wherein the first III-N material and the second III-N material materials occupy adjacent lateral regions or islands interfacing the III-N spacer and the gate dielectric.