In order to study the reaction mechanism of insitu formation of silicon carbide (SiC), the carbon was deposited on the crystalline silicon (c-Si) substrate at high temperature of 400-600 °C using ultra-high-vacuum ion beam sputtering. X-ray diffraction, Raman spectra, Auger electron spectroscopy and high resolution scanning electron microscopy (SEM) with the attached dispersive X-ray (EDX) detector were used to examine the effect of substrate temperature on the reaction mechanism. Amorphous carbon was formed at room-temperature deposition and increased its disorder state with increasing deposition temperature to 500 °C corresponding to higher ratio of disorder peak to graphite peak intensity in Raman spectrum. The crystalline silicon carbide (c-SiC) was formed at 600 °C from the diffracted SiC(111) peak, which is much lower than conventional CVD c-SiC formed at more than 1000 °C. Also, a nanoweb-like morphology of c-SiC was observed on the surface from the SEM image. The atomic composition ratio of Si to carbon was about 54/46 from EDX analysis. Thermal energy is the diving force for the crystalline SiC formation through the interdiffusion between carbon and c-Si. The nanoweb-like morphology may be attributed the high surface energy of SiC with strong Si-C bonding.