Silicon carbide fibers are produced by mixing discontinuous isotropic carbon fibers with a silica source and exposing the mixture to a temperature of from about 1450 C. to about 1800 C. The silicon carbide fibers are essentially devoid of whiskers have excellent resistance to oxidation and excellent response to microwave energy, and can readily be formed into a ceramic medium employing conventional ceramic technology. The fibers also may be used for plastic and metal reinforcement.