In　this　paper,　new　electrothermal　characteristics　degradation　and　failure　mechanism　of　Silicon　carbide　junction　barrier　Schottky　(SiC　JBS)　devices　with　different　die　attach　materials　under　300°C　power　cycle　stress　were　investigated　and　found　based　on　thermal　structure　function　and　failure　analysis.　The　results　showed　that　the　electrothermal　characteristics　(thermal　resistance,　Rth　j-d　and　on-resistance,　Ron)　were　consistent,　which　were　different　in　that　decreased　firstly　and　then　increased　for　nanosilver,　but　increased　overall　for　alloy　solders　under　300°C　PC,　both　strongly　related　to　evolution　of　porosity,　secondphase,　interface　cracks,　grain　size　in　the　die　attach　layer.　However,　the　electrothermal　characteristics　were　affected　by　dieattach　evolution　to　varying　degrees　due　to　different　diffusion　mechanisms,　causing　different　failure　phenomena　(50,　1200　and　4000　failure　cycles　for　high-lead,　Au-Ge　solder　and　nanosilver　respectively).　Meanwhile,　the　reverse　leakage　current　(IR)　and　breakdown　voltage　(VR)　variations　mainly　depended　on　chip　interface　states,　including　the　Schottky　barrier　lowering　effect　(induced　by　AlW　IMC　and　large　cracks　generated　at　the　Schottky　contact　metal　layer/chip　interface)　and　electrons　and　holes　trapped　at　the　SiO2/4H-SiC　interface　in　the　termination　zone.　Finally,　this　article　discussed　three　failure　mechanisms　observed　in　devices　employing　three　die　attach　materials　under　300°C　PC.　IEEE