Commercially available (001) InP substrates have been treated by exposure to UV/ozone to produce surface oxide layers suitable for thermal desorption prior to epitaxial growth. Thermally induced changes in composition and structure of the oxidized surfaces in vacuum have been studied using Auger electron spectroscopy (AES), reflection high-energy electron diffraction (RHEED), and Rutherford backscattering/channeling (RBSC). It is found that for temperatures above 440–450 °C the oxide becomes unstable. Thermal oxide desorption in vacuum above 460 °C always results in a P-depleted surface. At 460 °C the oxide can be thermally removed without noticeable P loss; however, the time requried for this process is approximately 2 h. Time-dependent AES results for oxide desorbing at a fixed temperature can be described by assuming a thinning process with a constant thinning rate for short annealing times; however, for longer times the desorption rate increases considerably. After complete oxide removal, the resulting clean (001) InP surface shows a 2 × 1 RHEED pattern, while the corresponding measured In surface peak intensity as measured by RBSC is close to that obtained for a clean MBE grown surface. Significant structural deterioration of the surface is detected at high temperatures (≈ 495 °C) by RHEED nad RBSC. The average O/In composition ratio of the oxide layer has been determined by ion scattering methods.