A combination of measurements of electrical resistivity, Hall mobility, and phosphorus concentration by secondary ion mass spectroscopy has determined the value of the Hall scattering factor in P‐doped epitaxially grown Si. The Hall scattering factor is found to increase from a value close to unity at a P concentration around 1017cm−3, to ∼1.3 in the 1018–1019cm−3doping range. At higher doping levels it decreases and saturates to a value of ∼0.9 for doping levels higher than 1020cm−3.