The Si-O-C-H composite thin films were deposited on a p-type Si(100) substrate using bis-trimethylsilane (BTMSM) and O-2 mixture gases by an inductively coupled plasma chemical vapor deposition (ICPCVD). High density plasma of approximately similar to 10(12) cm(-3) is obtained at low pressure (< 320 mtorr) with an RF power of approximately 300 W in the inductively coupled plasma source where the BTMSM and oxygen gases are greatly dissociated. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra show that the film has Si-CH3 and O-H related bonds. The CH3 groups formed the void in the film and the Si atoms in the annealed sample have different chemical states from those in the deposited sample. It means that the void is formed due to the removing of O-H related bonds during the annealing process. The relative dielectric constant of the annealed sample;with the flow rate ratio O-2/BTMSM as 0.3 at 500 degreesC for 30 min is approximately 2.5.