Si nanowires synthesized by the thermal evaporation of a silicon monoxide powder or a mixture of silicon and silica powders burned fiercely in air and exhibited a large photoacoustic effect when exposed to a conventional photographic flash. The energy required to ignite the Si nanowires was 0.1−0.2 J/cm2. Si nanowires showed a strong ability to confine energy from visible light. The remaining material obtained after burning Si nanowires consisted of various forms of nanostructures (e.g. nanoparticles, amorphous wires, and nanotubes).