To　measure　the　junction　temperature　of　diodes　under　operating　conditions,　the　temperature　calibration　curve　is　studied　under　large　current　conditions.　To　avoid　the　self　heating　by　the　large　current　conditions,　pulsed　currents　are　used　in　the　paper.　The　temperature　calibration　curve　of　TO-247-2L　fast　recovery　diode　is　investigated　in　this　paper.　The　0-1.5　A　pulse　current,　of　which　the　pulse　width　is　250　mu　s　and　the　duty　cycle　is　5%,　is　chosen　to　study　the　temperature　calibration　curves　under　50,　70,　90,　110,　130　degrees　C　respectively.　The　results　show　that　under　the　large　current　condition,　the　temperature　calibration　curve　bends.　The　main　reason　for　the　bending　phenomenon　is　that　the　series　resistance　changes　with　temperature　increasing,　which　is　affected　by　the　mobilities　of　electrons　and　holes　in　semiconductor　material.　With　the　temperature　rising,　the　mobility　decreases,　which　results　in　the　increasing　of　series　resistance.　Due　to　the　series　resistance　increasing　The　voltage　on　p-n　junction　will　be　reduced.　For　this　reason,　a　higher　voltage　is　needed　to　obtain　the　same　current,　and　the　temperature　calibration　curve　will　bend.　There　are　two　reasons　which　will　lead　to　the　temperature　rising.　The　first　reason　is　self-heating　of　devices　by　the　power　dissipation,　and　the　second　reason　is　that　the　temperature　of　device　is　heated　by　ambient　temperature.　Under　the　same　temperature,　self-heating　behaviors　of　device　by　different　currents　will　result　in　different　series　resistances.　But　in　the　paper,　the　results　show　that　the　series　resistances　under　different　currents　are　the　same,　which　illustrates　that　self-heating　is　not　the　key　reason　for　the　change　of　series　resistance.　So,　the　temperature　changing　of　the　diode　is　caused　by　the　ambient　temperature　rising,　which　verifies　that　the　bending　phenomenon　of　the　temperature　calibration　curve　of　TO-247-2L　fast　recovery　diode　is　caused　by　the　ambient　temperature　rising.　Then,　through　experimental　measurements　and　theoretical　calculations,　the　accurate　nonlinear　temperature　calibration　curve　is　acquired,　which　can　reduce　the　measurement　errors　of　high　current　transient　junction　temperature.