Nanocrystalline cubic silicon carbide (3C-SiC) films embedded in an amorphous SiC matrix were fabricated by the hot-filament chemical-vapor-deposition technique using methane and silane as reactance gases. High-resolution transmission electron micrographs clearly showed that these films contain naoncrystallites, with an average dimension of about 7 nm, embedded within an amorphous matrix: X-ray photoelectron spectroscopy, x-ray diffraction, infrared absorption, and Raman scattering studies revealed the nanocrystallites as having the structure of that of 3C-SiC. In contrast to 3C-SiC, where no photoluminescence could be observed at room temperature, strong visible emission with a peak energy of 2.2 eV could be seen from the nanocrystalline films at room temperature. The presence of nanocrystalline cubic SiC in these films is believed to result in a change in their energy-band structure, compared to that of 3C-SiC, which promotes radiative recombination of electron-hole pairs.