Binary nonoxide additives ZrSi2-MgSiN(2)were applied to obtain Si(3)N(4)ceramics with high thermal conductivity by gas pressure sintering. The shrinkage behaviors during sintering were investigated by in situ dilatometry. Although densification was retarded due to a higher N/O ratio in the liquid phase, the incorporation of oxygen was inhibited because of the lower oxygen content in the liquid phase. The substitution of oxide additives by nonoxide additives eliminated native SiO(2)and induced a nitrogen-rich liquid, resulting in purified Si(3)N(4)grains, reduced glassy phase, and enhanced Si3N4-Si(3)N(4)contiguity. Ultimately, a thermal conductivity of 117.32 W m(-1) K(-1)was achieved using ZrSi2-MgSiN(2)as sintering additives, increased by 32% compared to those doped with ZrO2-MgO.