We investigated the fabrication of Si nanocrystals, including thin films, by annealing the SiO/C/SiO thin films in an Ar atmosphere. The SiO/C/SiO trilayered thin films were deposited on α-Al2O3 (0001), Si (111), or ITO-coated borosilicate glass substrates at room temperature by pulsed laser deposition using dual sintered SiO and graphite targets. The SiO/C/SiO thin films subjected to heat treatment at 500°C included nanocrystalline Si. Measurements by synchrotron radiation X-ray diffraction indicated the formation of Si nanocrystals having a size of 5–10 nm. Fourier transform infrared spectra showed that Si–O stretching and vibrational peak intensities of the as-deposited thin film decreased remarkably after annealing. The C layer in the SiO/C/SiO trilayered thin films is considered to play a role in enhancing the chemical reaction that produces Si nanocrystals through reduction of SiO during heat treatment. The annealed SiO/C-based thin films, including Si nanocrystals, exhibited photosensitive conduction behavior in current–voltage measurements.