Reports on the characteristics of a major defect in mass-produced silicon carbide wafers which severely limits the performance of silicon carbide power devices. Micropipe defects originating in 4H- and 6H-SiC substrates were found to cause pre-avalanche reverse-bias point failures in most epitaxially-grown pn junction devices of 1 mm/sup 2/ or larger in area. Until such defects are significantly reduced from their present density (on the order of 100's of micropipes/cm/sup 2/), silicon carbide power device ratings will be restricted to around several amps or less. >