AbstractDevices fabricated from the wide bandgap semiconductor SiC have many advantages over those made from conventional semiconductors. Thus, performance characteristics of some 4H-SiC devices can be two orders of magnitude better than equivalent devices made from silicon. On the other hand, new and unexpected problems have emerged with the operation of some SiC devices that need to be understood and solved before further progress can be made in this area. One of the most intriguing problems has been the degradation of bipolar PiN diodes that have major advantages over unipolar Schottky barrier diodes at high blocking voltages. The electrical degradation of the PiN diodes refers to a drop in voltage under extended forward current operation. The degradation appears to be associated with the appearance of stacking faults (SFs) in the entire base region of the diode. In this paper, we discuss some puzzling aspects of stacking fault formation in such diodes. Electroluminescence as well as TEM has been used to investigate the degradation problem and, based on experimental results, the formation of stacking faults within the device, possible sources of partial dislocations responsible for the stacking faults, and the enhanced motion of dislocations under forward biasing are considered.