This paper focuses on the use of infrared spectroscopic ellipsometry (IRSE) to characterise thin organosilane films deposited on aluminium. IRSE combines in one measurement the possibilities of traditional FT-IR methods (molecular information) with those of visible spectroscopic ellipsometry (SE) (morphological-film thickness and optical-refractive index/extinction coefficient information). In this study, this optical method is used to get relevant informations concerning the influence of a thermal curing on various characteristics of the silane films. It will be shown that, by using an appropriated optical model for the interpretation of the data, IRSE permits to determine quantitatively the curing effect on the film thickness, non-uniformity and chemistry. It will be also demonstrated that the results obtained from the IRSE analysis correlate well those obtained from SE and electrochemical impedance spectroscopy (EIS). (C) 2003 Elsevier Science B.V. All rights reserved.