The subband dispersions in the Si(1 1 1) p-type inversion layers induced by Pb and Ga adsorbed surface structures were measured by angle-resolved photoemission spectroscopy (ARPES). The surface structures used here were Si(1 1 1)3 root 3 x 3 root 3-PbGa and Si(1 1 1)6.3-Ga. Si(1 1 1)3 root 3 x 3 root 3-PbGa is a new surface phase found in this study. Because it is significant in our study to investigate potential effects of surface superstructures on the hole subband dispersion, we investigated the subband energy levels quantitatively comparing them with those calculated using the triangular approximation. It was found that the energy separation of the adjacent subband quantum levels in the inversion layers induced by gallium adsorption does not follow the triangular approximation. The possible band bending shape was proposed to explain the quantum level spacing of the subbands in Ga-induced inversion layers. (C) 2008 Elsevier B.V. All rights reserved.