The optical properties of 1-methyl-1,2,3,4,5-pentaphenylsilole thin films grown on silicon substrate were investigated using spectroscopic ellipsometry SE. Accurate refractive index n and extinction coefficient k, in the wavelength range of 250 to 800 nm, were determined. Sellmeier equations, amorphous semiconductor model, and a three-oscillator classical Lorentz model were used to fit the data in different spectral ranges. A band gap of 2.78 eV and uv absorption peaks at 368 and 263 nm were derived from the SE spectrum. Additionally, the absorption spectra near the major band edges show optical properties similar to that of an amorphous semiconductor. © 2002 American Institute of Physics.