Abstract: A reactively combined silicon nitride is produced in which the starting material is pure silicon powder or a powder mixture of pure silicon and its nitride. This material is subjected to cold isostatic pressing or a slip casting or diecasting process before it is brought into a hot isostatic mold. The reaction is triggered under a nitrogen pressure of initially 0.5-2.0 MPa and at a starting temperature of 1000.degree. C. During the reaction the pressure is raised to 4.9 MPa and the temperature to at most 1420.degree. C. This raising of pressure and temperature is carried out at least partially stepwise. Obtained thereby is a product having a degree of nitriding greater than 92%. With a cycle time of less than 24 hours, the process permits molded articles to be produced which have a wall thickness of more than 10 mm, the material being uniformly nitrided.