Combining Rutherford backscattering spectroscopy (RBS), X-ray photoemission spectroscopy (XPS) and X-ray Auger spectroscopy, we have studied thin films of Bi2Sr2CaCu2O8 + δ deposited by laser ablation on oriented MgO(100) single crystals. RBS and XPS indicate the absence of interdiffusion into the substrate and continuity of the films. On heating the films in vacuum up to the fusion temperature (880°C), oxygen losses are observed and correlated with the disappearance of formal Cu3+, with the strong decrease in oxidized (hole-doped) oxygen and with a metal- semiconductor phase transition. An appreciable percentage of formal Cu3+ (about 24%) is estimated from the analysis of the Auger Cu L3VV spectrum in contrast to the ceramic case where formal trivalent copper is not present. This is likely because the thin film (textured) structure allows the retention of more excess oxygen than the surface of the ceramic grains. We suggest that Cu3+ appears under the form of 3d9L and 3d10L2 configurations, instead of 3d8, consistently with the formation of p holes (L, L2) in the valence band.