The silicon powder is used as a raw material, and the desired shape is first formed by a usual molding method, and preliminary nitriding is performed in a nitrogen gas at a high temperature of 1200 ° C, and a part of the silicon powder is reacted with nitrogen to form Silicon Nitride
, and the entire billet is then formed. The body already has a certain strength. Then, a second nitriding is carried out in a high temperature furnace at 1350 ° C to 1450 ° C to form a silicon nitride. A silicon nitride having a theoretical density of 99% can be obtained by a hot press sintering method.