RON and VTH drifts in TO-247 SiC packaged MOSFETs are investigated in this paper. The use of a novel on-the-fly measurement setup able to capture their variation over a 100μs to 1000s time range revealed the presence of two separated fast and slow mechanisms affecting the VTH and RON stability. Particularly, fast drain-induced mechanisms were found to negatively shift VTH, whereas no appreciable fast drifts were observed on RON. Conversely, slow drifts were found on both parameters, yielding a decrease in VTH and an RON increase. To investigate their origin, measurements were carried out for either i) different Duty Cycles and ii) several on-state current levels, proving that device self-heating (i.e., temperature increase) is responsible for the observed slow instabilities.