We have investigated the annealing of vacancy-type defects and B diffusion in SiC using positron annihilation spectroscopy (PAS) and secondary ion mass spectroscopy (SIMS). Boron (B) and carbon (C) ions were implanted into 6H-SiC substrates, and the samples were annealed up to 1650 degreesC in Ar. In the PAS study, defective layer to a depth of 200 nm from the surface is observed after annealing between 800 and 1200 degreesC. This region disappears after annealing above 1500 degreesC. No significant difference in the annealing behavior of the vacancy-type defects is observed for only B-and C/B-implanted samples. In the SIMS study, the out-diffusion of B in 6H-SiC is observed after annealing above 1400 degreesC and a dip in the B concentration is created close to the surface. This out-diffusion of B is suppressed by C/B-implantation. This suppression tends to be enhanced by the temperature of the implantation and the concentration of the implanted C.