Poly(dimethylsilylene-diphenylsilylene) copolymer, [(SiMe₂) _χ(SiMe₂)]_n, where x=1.0 to 8.0, was synthesized by condensation polymerization of dimethyldichlorosilane and diphenyldichlorosilane in xylene. In the thermogravimetric analysis of the copolymer, weight loss started at 170 ℃ and the weight residue at 1,000℃ was 32%. The copolymer was stabilized by thermal oxidation at 80 to 110℃ for 5 hr in air, and its thermal stability increased as the temperature increased. The copolymer heat treated above 700℃ showed no organic bonds of C-H and Si-CH₃, while Si-C and Si-O bonds were observed. Amorphous SiC was obtained by Pyrolysis at 1,000℃ and β-SiC at 1,200 to 1,400℃, in which better crystallinity of β-SiC was observed at a higher temperature.