Single-crystal silicon films of sub-micrometer thicknesses were tensile tested using a thin film tensile tester with an electrostatic force grip. The tester has been newly designed for this thin film. It uses a servo-controlled balance for small-force measurement with a resolution of less than 100 νN. The specimens were fabricated using bulk- and surface-micromachining starting with a SIMOX wafer, and an epi-SOI wafer. The bulk micromachined specimens were released from a wafer by anisotropic etching from the backside of the wafer. The specimen size was 0 to 500 νm long, 20 or 50 νm wide and 0.14 νm thick. The thinner specimens were fabricated by surface micromachining and dry release process using XeF2 and vapor HF etching to avoid stiction of the specimens. The size was 0 to 600 νm long, 1 to 20 νm wide and 0.05 νm thick. These wafers were (100) oriented and the loading axis of the specimen was <110>. The tensile strength of the bulk micromachined specimens ranged from 1.4 to 4.8 GPa for twelve samples and that of the surface micromachined specimens ranged from 1.0 to 6.8 GPa for seven samples.