Silicon is one of the major constituents of the earth's crust and, in its elemental form, the base of many semiconductor applications, including electronics and energy conversion. Downsizing Si to the nanoscale dimension extends its application to diverse fields, which, however, is often plagued by expensive and inefficient fabrication methods. We report herein a facile chemical synthetic method for Si nanoparticles from SiO₂ in a liquid environment of molten metal chlorides containing magnesium. The results show that Si nanocrystals (NCs) start to grow at 550 °C in the molten salt solvent and that the growth is controllable through the adjustment of the temperature, as well as the type of salt. We also show that the method can be generalized, as illustrated by the synthesis of Ge nanoparticles at a temperature of 450 °C. The growth of NCs is interpreted in terms of the chemical reduction of oxide by electrons solvated in the molten salts.