Interface　states　modulated　reverse　leakage　current　through　metal/AlxGa1-xN/GaN　diodes　has　been　studied.　Reverse　leakage　current　and　breakdown　voltage　have　been　measured　over　wide　temperature　ranges.　The　investigation　suggests　that　the　piezoelectric　polarization　and　the　spontaneous　polarization　at　the　AlxGa1-xN/GaN　heterostructure　create　polarization　induced　charges　in　AlxGa1-xN,　and　influence　the　two-dimensional　electron　gas　at　the　GaN/AlxGa1-xN　interface.　Both　of　them　dictate　the　barrier　height　of　the　strained　AlxGa1-xN　Schottky　contact.　High　density　of　defect　states　at　the　metal/AlxGa1-xN　interface　leads　to　high　reverse　leakage　current　via　Fowler-Nordheim　emission　and/or　Frankel-Poole　emission.　The　most　notable　finding　is　the　reduction　in　the　leakage　current　almost　to　zero　at　high　temperatures　due　to　strain　relaxation,　reduction　in　defect　states,　and　barrier　height　enhancement　at　the　metal/AlxGa1-xN　interface.　Such　finding　may　have　significant　impact　on　the　way　we　design　high-power　microwave　devices.