PURPOSE: To obtain ceramic fibers with high durability and mechanical strength at elevated temperatures by providing the surface of core wire consisting of silicon nitride fiber with fine-crystalline, high-purity silicon carbide through chemical vapor growth process.

CONSTITUTION: Silicon nitride fiber ≤20μm in diameter is used as core wire. The wire is (A) cut into short wires with appropriate length and put into a CVD (chemical vapor deposition process reaction oven, or (B) fed at a constant velocity from one end of the CVD reaction oven to the other end thereof to make treatment in a continuous way. For the synthesis of SiC, respective feedstock gases as Si and C sources, e.g. SiCl4 and CH4 are introduced into the reaction oven and made to react at 1200-1500°C under a pressure of 1-500Torr. With this method, for example, the surface of the silicon nitride fiber 10 in diameter is provided with silicon carbide at 1300°C through CVD process to obtain the objective ceramic fiber 50μm in diameter. This fiber is stable in an inert gas atmosphere even at temperatures as high as about 2000°C and resistant to oxidation even at temperatures 4 as high as 1600°C in the air.