Chemical-mechanical polishing (CMP) has proven a powerful tool for the final polishing of semiconductor and compound semiconductor substrates such as silicon, sapphire, gallium arsenide, and indium phosphide. For these materials, conventional CMP techniques have been able to produce removal rates of several μm/hr while achieving pristine, epi-ready surfaces with subsurface damage less than 10[nm]. For certain materials of interest in the compound semiconductor community, particularly silicon carbide (SiC) and the III-V nitrides, conventional CMP techniques perform poorly. These materials are extremely chemically inert, negating the desired chemical effect leading to removal rates of less than 0.1[μm/hr]. These materials are also very brittle and take damage easily, so a significant amount of material must be removed to ensure a sufficiently low subsurface damage for epitaxy. This paper documents the improvements made in the CMP of 4H and 6H SiC by augmenting a colloidal silica slurry with chemical additives and with special treated nano size diamond particles. The chemical additives proved most effective on 4H SiC, enhancing the slurry’s chemical effect and improving its removal rate. For both materials, the addition of the diamond (Chemical-Mechanical Polish with Diamond, CMP-D) greatly enhanced the removal rate and provided strong synergy between mechanical strain and chemical effect resulting in low subsurface damage.