The electron density of a pure InSb crystal has been synthesized using very accurate x‐ray diffraction intensities. After subtracting the electron density of the palladium core from both kinds of atoms, the distribution of the valence electrons was determined. By this means it was established that, on the average, 0.45±0.05 electrons are transferred from the Sb atoms to In atoms, as compared to a transfer of 0.34 or 0.42 electrons deduced from infrared absorption measurements. The effective ionic charge to be used in polar‐scattering calculations for InSb was calculated to be 0.17±0.02 e based on the electron density, as compared to 0.18 e or 0.16 e determined from electron mobility measurements.