For the integration of strained Si1-xGex epilayers in future silicon technologies it is necessary to obtain flat planar interfaces. Thus, a good understanding of the growth mechanism and a good knowledge of the properties of this strained material are required. Many articles have dealt with these problems in the literature. In a previous study, atomic force microscopy (AFM) was used to analyze the morphological modifications in SiGe epilayers grown on Si. The different stages of surface evolution have been determined, particularly the onset of undulations. In this study, we have investigated these surface modifications using the contact angle measurement technique. We observed a correlation between the root mean square (RMS) values of the roughness obtained with AFM and the water contact angle values. We demonstrate that the contact angle measurement technique, taking certain precautions, allows the critical thickness, i.e. the thickness beyond which the undulation pseudo-period increases, to be determined accurately.