A method for synthesis of high surface-area (>100 m2/g) and nanosized (≦100 nm) silicon powder by initiation of self-sustained combustion reaction in a mixture of silicon dioxide and magnesium powders in a sealed reactor chamber under pressurized inert gas atmosphere. A specific feature of the method is rapid cooling of the product at a rate of 100 K/s to 400 K/s in the area directly behind the combustion front.