The ellipsometric parameters of LPCVD poly-Si on insulating SiO2 (Si SOI) before or after annealing with laser or RF inducting graphite strip heater were measured by speetroscopic ellipsometry over the wavelength interval 3000-5000?. The four-phase model of ellipsometric spectra was presented by matrix multiplication and the Monte Carlo simulation was used to calculate both ε1 and ε2 of Si SOI. The lattice perfec-tion of Si SOI after annealing is discussed