Stacking faults in SiC whiskers grown by three different growth mechanisms; vapor-solid(VS), two-stage growth(TS), and vapor-liquid-solid (VLS) mechanism in the carbothermal reduction system were investigated by X-ray diffraction(XRD) and transmission electron microscopy (TEM). The content of stacking faults in SiC whiskers increased with decreasing the diameter of whiskers, i.e., the small diameter whiskers (<1 $mu extrm{m}$) grown by the VS, TS, and VLS mechanisms have heavy stacking faults whereas the large diameter whiskers(>2$mu extrm{m}$) grown by the VLS mechanism have little stacking faults. Heavy stacking faults of small diameter whiskers was probably due to the high specific lateral surface area of small diameter whiskers.