A method of making a densified silicon nitride/oxynitride composite is disclosed. The method comprises: (a) shaping a substantially homogeneous powder mixture of silicon nitride, 6-18% yttrium silicon oxynitride of the Y.sub.10 Si.sub.6 O.sub.24 N.sub.2 phase in an amount to form a viscous solution with at least a portion of the silicon nitride, and (b) densifying the body by heat fusion, with or without the use of mechanical pressure, to a density and a dimension required for the final product.