Fundamentals　of　the　Schottky　contacts　and　the　higherature　current　conduction　through　three　kinds　of　Schottky　diodes　are　studied.　N-Si　Schottky　diodes,　GaN　Schottky　diodes　and　AlGaN/GaN　Schottky　diodes　are　investigated　by　I-V-T　measurements　ranging　from　300　to　523　K.　For　these　Schottky　diodes,　a　rise　in　temperature　is　accompanied　with　an　increase　in　barrier　height　and　a　reduction　in　ideality　factor.　Mechanisms　are　suggested,　including　thermionic　emission,　field　emission,　trap-assisted　tunnelling　and　so　on.　The　most　remarkable　finding　in　the　present　paper　is　that　these　three　kinds　of　Schottky　diodes　are　revealed　to　have　different　behaviours　of　higherature　reverse　currents.　For　the　n-Si　Schottky　diode,　a　rise　in　temperature　is　accompanied　by　an　increase　in　reverse　current.　The　reverse　current　of　the　GaN　Schottky　diode　decreases　first　and　then　increases　with　rising　temperature.　The　AlGaN/GaN　Schottky　diode　has　a　trend　opposite　to　that　of　the　GaN　Schottky　diode,　and　the　dominant　mechanisms　are　the　effects　of　the　piezoelectric　polarization　field　and　variation　of　two-dimensional　electron　gas　charge　density.　©　2009　Chin.　Phys.　Soc.　and　IOP　Publishing　Ltd.