In this paper, porous silicon (PS) layers of different porosity and thickness have been investigated by Raman spectroscopy. The estimation of built‐in strain in PS is reported. Moreover, wetting phenomena in PS layers have been also investigated. The results prove a reversible blue shift of Raman spectra of wetted PS layers with respect to unperturbed layers. We ascribe the shift to a compressive stress due to the increased lattice mismatch between the PS layer and the bulk silicon substrate in wetting conditions. Copyright © 2008 John Wiley & Sons, Ltd.