Sulphur from an electrochemical source has been used to dope GaSb grown by molecular‐beam epitaxy. The incorporation of sulphur in the epilayers has been measured by secondary ion mass spectrometry, and the effects of substrate temperature during growth and of the antimony‐to‐gallium flux ratio have been studied.The incorporation has been found to be a strong function of substrate temperature, varying from ∼100% below 435 °C to ∼1% at 525 °C. The incorporation also increases with antimony overpressure, varying by a factor of 3 on changing the antimony‐to‐gallium flux ratio from 1:1 to 4:1. The substrate temperature dependence is described by a simple kinetic model. The electrical activity of the incorporated sulphur is shown to be close to 100%.