For the purpose of high-yield fabrication of single-crystal-silicon cantilevers based on a silicon-on-insulator (SOI) wafer, the internal compressive stress effect of the BOX has been investigated. The large stress in the BOX is responsible for the BOX cracking at the end of the bulk etching. For the cantilevers with comparable thickness with the BOX in the authors’ experiments, the cantilevers break with the BOX cracking, which leads to the failure or low yield of the fabrication. Patterning the BOX has been proposed to release the stress and avoid the cantilever breaking. The yield based on this method is as high as 100%, and the cantilevers show high quality factor and force sensitivity in vacuum measurements. Patterning the BOX effectually ensures the high-yield fabrication of cantilevers, especially meaningful for the floppy cantilevers. The method proposed here is also promising for the high-yield fabrication of other floppy sensors based on a SOI wafer.