A combination of Xe-129 NMR measurements performed at different temperatures gives insight into the surface properties of an MCM-41 of unimodal porosity and of two SBA-15 silicas of bimodal porosity synthesized with (SBA-B) and without (SBA-A) a 373 K hydrothermal treatment. The signatures of xenon located either in disordered intrawall micropores or in mesopore surface defects are distinguished through the study of the temperature of xenon condensation. Even though the volume of micropores is reduced by hydrothermal treatment by nearly 60%. the remaining micropores could be very important to understand the sorption properties of SBA silicas because either their geometry or the hydrophobic character of their surface changes upon hydrothermal treatment.