We present the results of BeppoSAX observations of PKS 2155–304 during an intense \gamma –ray flare . The source was in a high X–ray state . A temporal analysis of the data reveals a tendency of the amplitude of variations to increase with energy , and the presence of a soft lag with a timescale of the order 10 ^ { 3 } s. A curved continuum spectrum , with no evidence of spectral features , extends up to \sim 50 keV , while there is indication of a flatter component emerging at higher energies , consistent with the interpretation of the broad band spectral energy distribution ( SED ) as due to synchrotron self–Compton ( SSC ) emission from a single region . Notably , the fitting of the SED with such a model is consistent with an interpretation of the detected soft lag as due to radiative cooling , supporting the idea that radiation losses play an important role in variability . The observed shifts of the SED peaks between the lowest and highest flux levels can be accounted for by an increase of the “ break ” energy in the relativistic particle spectrum . The model predicts emission at TeV energies in good agreement with the recently reported detection .