Electrochemical impedance spectroscopy (EIS) and Fourier Transform Infrared Attenuated Total Reflection (FTIR-ATR) Spectroscopy were combined as a spectroelectrochernical method to analyze water uptake of thin polymer films on semiconducting optical crystals. An oxide covered n-doped silicon crystal was used as optical crystal and an epoxy-amine adhesive was used as polymer film. The combined in-situ analytical approach allowed the analysis of diffusion coefficients of water with two independent measurement techniques, the quantification of the water uptake and its influence on the interphasial composition. The analytical approach is shown to be suitable for defect free polymer films and for defect containing polymer films. The corresponding semiconductor electrochemistry of silicon was evaluated to analyze the film capacitance in series with the semiconductor space charge capacitance. (C) 2007 Elsevier Ltd. All rights reserved.