This letter reports a measurement of the mean electron‐hole pair creation energy in crystalline silicon using photons in the 50–1500 eV spectral range. A cryogenic electrical substitution radiometer in combination with monochromatized synchrotron radiation was used to determine the spectral responsivity of silicon photodiodes in this spectral range with a relative uncertainty of less than 0.3%. The mean electron‐hole pair creation energy has been determined from these measurements and in contrast to recent theoretical and experimental results a constant value of (3.64±0.03) eV was obtained in accordance with a calculation presented here. ©1996 American Institute of Physics.