In a view of the importance of the solid-state properties of the oxide/hydroxide films on the efficiency of Ni-catalysts, this work is focused on the electronic structure of the passive alpha-Ni(OH)(2) film that behaves as an n-type semiconductor (with anion vacancies as dominant point defects). The solid-state transformation of the n-type alpha-Ni(OH)(2) film to Ni was discussed in the terms of Gerischer's approach for a reductive decomposition of a classical semiconductor. The kinetics of the alpha-Ni(OH)(2) decomposition to Ni was studied in situ and the decomposition mechanism was proposed. The nickel metal nucleation begins at the anion vacancies on the film vertical bar solution interface and finally the whole oxide film matrix transforms to the new metallic phase. The hydrogen evolution reaction (h.e.r.) takes place at a potential more positive than E-r(H-2/H+) at a freshly, in situ extracted Ni surface. The semiconducting properties of the passive film were compared to those of an oxide film, also n-type semiconductor that is formed on Ni by ion-implantation method. The latter film mentioned shows compact, more ordered and less amorphous structure than the first one what is in accordance to the X-ray photoelectron spectroscopy (XPS) results. (C) 2015 Elsevier B.V. All rights reserved.