Young’s moduli of single crystalline silicon in three major directions are measured by direct uniaxial tension tests using a microscale beam specimen. The 10 μm thick, 50 to 100 μm wide and 6 mm long tension specimens are micromachined along the three major crystal directions from two different types of silicon-on-insulator (SOI) wafers, (100) top layer and (110) top layer. A uniaxial tension loading frame is custom-built for the testing. Stress and strain are measured using a commercial load cell and a laser interferometry system, respectively. Measured Young’s moduli in 〈100〉, 〈110〉, and 〈111〉 directions are 115.3, 169.2, and 191.1 GPa, respectively. Expected to be insensitive to the sample size or fabrication method, Young’s moduli of single crystalline silicon can be a good measure of the reliability of microspecimen tension test systems.