[en] Highlights: • A facile method to prepare Si nanocrystals is developed by annealing a photoresist. • Si nanocrystal thin film thus made possesses higher spatial density and light emission intensity. • A small turn-on voltage of electroluminescence of 3.8 V is also obtained. We report a facile method to prepare thin film of Si nanocrystals embedded SiO₂ (Si-NC:SiO₂) by annealing a photoresist of hydrogen silsesquioxane (HSQ) at 1100 °C in nitrogen via a phase separation process. The spatial density, photoluminescence intensity, the photoluminescence efficiency and electroluminescence intensity of Si-NC of the sample made from HSQ, or HSQ sample, were 15.0, 5.5, 1.5 and 7.9 times as large as those of the sample made by a traditional method of annealing SiO_x (1xx sample, respectively. Meanwhile, the turn-on voltage of electroluminescence of the HSQ sample was only 3.8 eV, which was more than 2 times smaller than that of the SiO_x sample. The results of this work may find application in developing high brightness Si light sources.