γ-Al2O3 layers fabricated by annealing-induced crystallization of ALD-grown amorphous (a-) Al2O3 films were studied using near-edge-X-ray absorption fine structure, soft X-ray reflection spectroscopy, photoelectron spectroscopy, internal photoemission spectroscopy, and X-ray diffraction method. Despite the crystallization at high (1100 °C) temperature expected to deliver a thermodynamically stable Al2O3 phase, the development of oxygen deficiency upon room-temperature deposition of TiN and TaN electrodes was established. We ascribe this effect to oxygen scavenging by chemically active metals such as Ti and Ta during electrode sputtering. As a result, a high density of gap states is generated in the insulating oxide near the metal surface, which may impair insulating properties of γ-Al2O3.