The smooth 2H–SiC fibers with hexagonal structure and a small amount of tower-like 3C–SiC fibers with face-centered cubic structure were synthesized with a simple catalyst-free method. Specifically, SiC fibers were obtained by thermal treatment of the Si₃N₄ powder in a graphite crucible at temperature of 1800 °C and pressure of 190 MPa in Ar atmosphere. The synthesized SiC fibers consist of SiC wires with several tens to hundreds of micrometers in length and mostly 200–800 nm in diameter and some SiC whiskers with shorter length of 3–15 μm. The smooth 2H–SiC fibers and rough 2H–SiC fibers with tower-like growth traces grown along [1010] direction, and the tower-like 3C–SiC fibers may grow with orientation attachment patterns along [111] direction. Finally, the vapor-solid growth mechanism and detailed growth process of SiC fibers were discussed.