Ultra-high　density　of　parallel　planar　defects　is　discovered　within　WC　grains　in　V-doped　cemented　carbide.　High　resolution　transmission　electron　microscopy　(HRTEM)　shows　that　such　defects　are　stacking　faults　on　the　{10　(1)　over　bar0}　prismatic　planes.　The　presence　of　multiple　stacking　faults　within　WC　grain　gives　rise　to　a　series　of　anomalous　diffraction　patterns,　including　the　streaking　of　diffraction　spots　and　forbidden　fractional　diffraction　spots.　Interestingly,　quantitative　analysis　indicates　that　the　density　of　stacking　faults　within　the　V-doped　sample　is　one　order　of　magnitude　higher　than　that　of　the　Ti-doped　counterpart.　Because　the　two　doped　samples　are　processed　under　the　same　condition,　we　conclude　that　the　planar　defects　of　WC　grains　in　V-doped　samples　are　largely　produced　during　the　sintering　of　cemented　carbide.　Aberration-corrected　TEM　images　suggest　that　the　formation　of　stacking　faults　can　be　ascribed　to　the　merging　of　independently　developed　WC　micro-pillars.　The　formation　of　such　pillars　can　be　further　explained　by　the　segregation　of　V-rich　precipitates　at　the　corners　between　basal　and　prismatic　planes.　The　current　finding　not　only　unravels　a　new　formation　mechanism　of　stacking　faults　within　WC　grains,　but　also　provides　a　new　route　to　design　superhard　cemented　carbides　with　interlaced　stacking　faults　by　simply　doping　solute　atoms　and　controlling　the　sintering　process,　other　than　the　traditional　deformation　method.