This paper is focused to the study of the stabilization of the photoluminescent properties of porous silicon (PS). For this purpose, as-formed PS samples were subjected to different surface treatments. Photoluminescent excitation spectra were used to obtain the indirect band gaps, yielding practically the same values for PS films having undergone different surface annealing and post-etch treatments. However, the excitation spectra show a significant blueshift with aging for the different samples, which has been related to the initial amount of oxygen present in the porous surface as detected by XPS and FTIR. The variation of the intensity of the excitation spectra with aging has also been studied and can be associated to carbon contamination. The results are interpreted in terms of quantum size effects in PS and the influence of the surface composition.