A　novel　on-the-fly　repetitive　short　circuit　(RSC)　ageing　system　under　different　gate-source　voltage　bias　(VGS)　is　designed.　The　static　behaviors　of　SiC　planar-gate　MOSFET　C2M0080120D　and　SiC　trench-gate　MOSFET　SCT3080KL　under　the　low　and　high　VGS　biases　RSC　ageing　are　quantitatively　and　experimentally　compared　for　the　first　time.　A　bidirectional　threshold　voltage　shift　with　different　degradation　rates　in　both　types　of　devices　is　observed.　The　smaller　change　of　SiC　trench-gate　MOSFET　SCT3080KL　is　observed　compared　to　SiC　planar-gate　MOSFET　C2M0080120D　under　low　and　high　VGS　biases　RSC　ageing.