A modified four-step method has been developed to grow a void-free 3C-SiC film of high quality on Si(100) in a mixed gas of SiH4−C3H8−H2 using low pressure chemical vapor deposition. A diffusion step was added after the carburization step in the traditional three-step method (clean, carburization, growth), and no cooling between each step was required. X-ray photoemission C 1s spectra support that the formation of SiC bonds can be greatly improved in the as-carburized Si(100) surface after diffusion at 1350 °C for 300 s. A thick 3C-SiC film of good crystal quality was grown on the as-diffused SiC layer during the growth step, confirmed by both X-ray diffraction and electron diffraction data. Hall effect measurements were used to characterize the electrical properties of SiC films. All the SiC films are n-type. The Hall mobility and carrier concentration of a SiC film of 1.5 μm thick increase from 320 to 395 cm2/(V s) and from 1.6 × 1017 cm−3 to 2.7 × 1017 cm−3, respectively, when the diffusion step is added.