The interaction between metal atoms and near-surface semiconductor atoms from GaAs results in metal and Ga and As atoms intermixing, or solid solutions and new compounds formed during the metal deposition on the GaAs surface. Near-surface GaAs layer changes induced by non-loaded evaporator light emission in situ in vacuum were studied in this work. The GaAs near-surface layer state changes were followed by measurements of resistivity as a function of light intensity and duration of exposure, and of SAW amplitude and phase velocity variations. These measurements have been correlated with the structure and composition changes of the semiconductor native oxide layer. The GaAs surface changes were additionally studied with HEED and microscopy methods. They can be explained by diffusion of Ga and As atoms from the crystalline GaAs into the oxide layer, and back, caused by the plastic deformation, as well as the interaction between the Ga and the As atoms and residual gas in the vacuum chamber resulting in changing the thickness and composition of the oxide layer. (C) 2002 Elsevier Science B.V. All rights reserved.