White-light-emitting silicon nanocrystals (Si NCs) have been prepared from Si powder through a facile route including HF-HCl etching. Owing to a broad size distribution, the light emission spectrum covers the whole visible wavelength range with full width at half-maximum (FWHM) of 230 nm. Covalent attachment of octyl monolayers to the Si surface changes the physical nature of the NCs from a solid into a solvent-free liquid, and affords them high thermal stability of photoluminescence (PL) even under ambient conditions.