The normal mode of vibration of (111) GaAs wafers with a thickness below about 15 &mgr;m was found to depend strongly on the surface preparation and on the ambient atmosphere. This dependence was attributed to effects directly related to the surface stress &sgr;s. It was shown that &sgr;scan be evaluated from the natural frequency of vibration. The values of &sgr;s, in the ⟨110⟩ direction, for etched and unetched (111) GaAs wafers in room atmosphere were found to be 325 and 570 dyn/cm, respectively. It was further demonstrated that surface stress transients due to the adsorption processes (adsorption transients) can be determined by corresponding changes in the natural frequency of vibration.