Fine-diameter continuous SiC fibers are considered one of the most effective reinforcing fibers for advanced ceramic matrix composites, possessing significant application potential in aerospace and nuclear industries. Among them, near-stoichiometric SiC fibers characterized by a highly crystalline microstructure have garnered considerable attention due to their exceptional high-temperature resistance. However, influence of high-temperature sintering conditions on composition and microstructure of the fibers is still unclear. Here, influences of different sintering temperatures and durations on decomposition of the SiC_xO_y phase, grain growth and densification of the fibers were systematically investigated. It was found that decomposition of SiC_xO_y and densification of fibers occur progressively from surface to core. Notably, a specific sintering temperature of 1800 ℃ was identified as optimal, wherein growth of β-SiC grains effectively compensated for the pore defects resulting from the decomposition of SiC_xO_y phase, thereby achieving fiber densification. Conversely, excessively high sintering temperature might result in decomposition of β-SiC grains. Although extending sintering duration facilitated removal of residual oxygen within the fibers, it could cause accumulation of graphite phases at β-SiC grain boundaries, leading to an increase in pore defects within the fiber core. Finally, near-stoichiometric SiC fibers with highly crystalline microstructure were successfully fabricated through optimization of sintering conditions, possessing a composition of SiC_1.04O_0.02Al_<0.01. The β-SiC grains within the fibers were uniformly distributed with sizes ranging from 100 to 200 nm. The fibers exhibited a tensile strength of 1.88 GPa and a Young’s modulus of 373 GPa, accompanied by a high density of 3.1 g/cm³. The findings of this research provide a robust foundation for further improving comprehensive properties of SiC fibers.