We have focused on measurements of the surface stress in Si(111) as a function of 7 x 7 reconstruction by comparison with the hydrogen (H)-terminated Si(111) 1 x 1 surface. In order to obtain information on both the surface stress and the surface reconstruction simultaneously, we have combined the surface-curvature and the reflection-high-energy-electron-diffraction instrumentations in an identical ultrahigh vacuum system. The stress evolution shows a decrease of tensile stress corresponding to the formation of H-termination at the beginning of the atomic H exposure of Si(111) 7 x 7 surface. After the above treatment, a complete transformation of the surface structure occurs from the reconstructed surface to the 1 x 1 one. As a result, we find the H-terminated Si(111) 1 x 1 surface releases 1.7 N/m (=J/m(2)), or (1.4 eV/(1 x 1 unit cell)), of the surface energy from the strong tensile Si(111) 7 x 7 reconstruction. (C) 2015 Elsevier B.V. All rights reserved.