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A super heat-resistant silicon carbide fiber has an oxygen content of less than 0.1% by weight. In a process for producing the super heat-resistant silicon carbide fiber, a precursor fiber prepared by spinning a polycarbosilane having an oxygen content of less than 0.8% by weight is irradiated with

A super heat-resistant silicon carbide fiber has an oxygen content of less than 0.1% by weight. In a process for producing the super heat-resistant silicon carbide fiber, a precursor fiber prepared by spinning a polycarbosilane having an oxygen content of less than 0.8% by weight is irradiated with a radiation in an oxygen-free atmosphere or in vacuo to make the precursor fiber infusible. The infusibilized fiber is fired in an oxygen-free atmosphere or in vacuo at a temperature of from 1000°to 2200°C. without exposure to an oxidizing atmosphere; or stabilized in the same atmosphere at a temperature of from 300°to 600°C. without exposure to an oxidizing atmosphere and fired in an oxygen-free atmosphere or in vacuo at a temperature of from 1000°to 2200°C.

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A process for producing a silicon carbide fiber having an oxygen content of less than 1.0% by weight and a heat resistance of 1800°C. or above, which consists essentially of the steps of: a) preparing a precursor fiber by spinning a polycarbosilane having an oxygen content of less than 0.8% by weigh

A process for producing a silicon carbide fiber having an oxygen content of less than 1.0% by weight and a heat resistance of 1800°C. or above, which consists essentially of the steps of: a) preparing a precursor fiber by spinning a polycarbosilane having an oxygen content of less than 0.8% by weight; b) irradiating said precursor fiber from step a) with an ionizing radiation in an oxygen-free atmosphere or in vacuum to make the precursor fiber infusible; c) heat-treating said infusible fiber from step b) in the same atmosphere at a temperature of from 300°to 600°C. in the absence of an oxidizing atmosphere to stabilize said infusible fiber; d) exposing said stabilized infusible fiber from step c) to air; e) and firing said stabilized infusible fiber from step d) in an oxygen-free atmosphere or in vacuo at a temperature in the range of from 1000°to 2200°C., with the proviso that the temperature-raising rate in the firing is 100°C./hr or less at least when the temperature is in the range of 1000°to 1100°C.