A fully dense SiC ceramic with a room-temperature thermal conductivity of 262 W(mK)(-1) was obtained via spark plasma sintering -SiC powder containing 0.79 vol% Y2O3-Sc2O3. High-resolution transmission electron microscopy revealed two different SiC-SiC boundaries, that is, amorphous and clean boundaries, in addition to a fully crystallized junction phase. A high thermal conductivity was attributed to a low lattice oxygen content and the presence of clean SiC-SiC boundaries.