The　avalanche　ruggedness　of　power　devices　becomes　a　crucial　issue　to　ensure　the　safe　operation　of　the　power　conversion　systems,　particularly　under　the　extreme　temperature　conditions.　In　this　article,　the　avalanche　capability　of　SiC　planar/trench　MOSFETs　is　systematically　evaluated　and　analyzed　over　the　temperature　range　of　90　to　340　K.　Importantly,　the　essential　mechanisms　and　temperature　dependence　of　avalanche　failure　under　cryogenic　conditions　are　further　explored　by　combining　many　analysis　methods　such　as　TCAD　simulations,　the　unclamped　inductive　switching　characterizations,　and　the　transient　junction　temperature　prediction.　The　highest　avalanche　energy　density　of　171.24　mJ/mm2　at　90K　indicates　the　great　application　potential　of　SiC　planner　mosfet　in　cryogenic　electronics.　Moreover,　the　safe　avalanche　operation　boundary　(AOB)　model　is　established　over　the　cryogenic　temperature　range.　The　relevant　analysis　method　and　AOB　model　can　be　used　to　accurately　evaluate　and　quantitatively　predict　the　avalanche　capability　of　SiC　planar/trench　mosfets　for　the　cryogenic　converter　design.　©　1986-2012　IEEE.