A fully dense SiC ceramic with high thermal conductivity was obtained by conventional hot pressing, with 1vol% Y2O3-Sc2O3 additives. The ceramic had a bimodal microstructure consisting of large and small equiaxed SiC grains. Observation with high-resolution transmission electron microscopy (HRTEM) showed two kinds of homophase (SiC/SiC) boundaries, that is crystallized and clean boundaries, and a fully crystallized junction phase. The thermal conductivity of the SiC ceramic was 234W(mK)(-1) at room temperature. The high thermal conductivity was attributed to a clean SiC lattice and good contiguity between SiC grains.