Fundamentals　of　the　Schottky　contacts　and　the　high-temperature　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　high-temperature　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.