Desorption of Sb from Si 1Àx Ge x layers (x ¼ 0, 0.05, 0.1, 0.2, 1) grown by molecular beam epitaxy (MBE) on Si(1 0 0) substrates is investigated using Auger electron spectroscopy thermodesorption (TD-AES). Sb desorption process on Si 1Àx Ge x is well described by a first-order reaction. No extra TD-AES peaks are observed on Si 1Àx Ge x compared to Si. For 1 ML of Sb coverage the TD-AES peak shifts to lower temperature when Ge bulk concentration increases. The Sb monolayer desorbs at 801, 752, 740, 715, and 706°C for x ¼ 0, 0.05, 0.1, 0.2 and 1, respectively. We explain the non-linear decrease of the Sb desorption energy when x increases by the strong Ge surface segregation during the MBE growth of Si 1Àx Ge x layers, resulting in an almost pure Ge surface even for low x.