This paper presents the results showing the effect of adding varying amounts of additives, such as NH 4 Cl, NaN 3 , and NaCl on the ratio of α/β-Si 3 N 4 prepared by nitridation of micrometer size silicon powder by combustion synthesis. The nitridation process was performed under 6.0MPa pressure of nitrogen, and the content of α/β-Si 3 N 4 in the final product was examined using intensity of the peaks in the XRD patterns. The resultant was a mixture of α-Si 3 N 4 and β-Si 3 N 4 , where a rapid increase of α-phase was found after addition of NaCl. In the optimized synthesis conditions, micrometer size Si 3 N 4 powder with ∼90% of α-phase was obtained. The reaction mechanism is discussed with respect to the combustion temperature and the amount of NaCl.