The authors have identified oxidation and desorption processes of Ge native oxide by chemical bonding states measured by X-ray photoemission spectroscopy. Ge oxidation occurs at the temperatures of 450–500°C in an oxidizing ambient. Ge desorption in nitrogen ambient is observed at the temperatures of 500–550°C, which is higher than the oxidation temperature by 50°C. Combined oxidation and desorption processes proceed subsequently and cause a loss of Ge from the surface when Ge is annealed in oxidizing ambient at a temperature higher than desorption temperature. The surface loss is avoided when Ge is annealed with SiO 2 cap layer in an identical annealing condition.