Photoluminescence (PL) from SiOx (0<χ<2) thin films, prepared byevaporation of SiO powder onto the Si (100) substrate followed by thermal annealing, was investigated for various film thickness and annealing temperatures. For the film thickness ranging from 120 to 700nm and annealing at 1100℃ for 30 min in nitrogen, the Si nanocrystals (nc-Si) embedded in SiO2 matrix were formed due to the phase separation process, and the PL of nc-Si exhibited a continuous red-shift with increasing film thickness in an exponential decay manner. This thickness dependence was explained by a model modified from that of Zacharias and Streitenberger (2000 Phys. Rev. B 62 8391) regarding the nucleation barrier for Si clusters versus their distances away from the substrate. Further, for the film thickness of 270nm and annealing temperature ranging from 700 to 1100℃, it was found that a green/yellow PL structure developed at elevated annealing temperatures, which reached the maximum in intensity at 900℃, and then dropped down for higher annealing temperatures. This PL emission was identified as due to the structural defects mainly consisting of oxygen vacancies in SiO2 matrix.