Co-doped SiC films are fabricated on Si (100) substrates by radio frequency magnetron sputtering, and the crystal structure, composition, element valences, local structure, and photoluminescence of the films are studied. Crystal structure analysis identifies the film structure as 3C-SiC and shows that the Co dopant atoms form CoSi secondary phase compounds in the films. The composition and element valence analysis show that the Co dopant atoms substituting for C sites in the SiC lattice exist in the form of Co2+ ions, and that C clusters are present in the films, which increase in amount with increasing Co dopant concentration. The analysis of local structure reveals that Co clusters, CoO and Co3O4, are not present in the films, and CoSi secondary phase compounds exist. All of the films show a violet photoluminescence peak located at 413 nm, which becomes stronger with increased Co dopant concentration and annealing temperature, and is found to originate from the C clusters.