The hysteretic thermal behavior of two amorphous semi-aromatic polyamides, Subjected to cyclic loading at high stress levels, has been investigated. The two polymers, called I I and 1.8T. were selected with regards to chain mobility and plastic deformability considerations. This work reports the exothermal response of these materials to high level cyclic stress (of the order of sigma(y)), with emphasis on the initial thermal peak, normally observed in commercial polycarbonate (PC) and not in commercial polymethylmethacrylate (PMMA). The investigated materials exhibit noticeable initial thermal peaks, which are similar, to some extent, to those observed in PC. The present results suggest that chain mobility may indeed be partially responsible for the initial exothermal peak. thus Supporting the hypothesis that it may be related to the transition from shear deformation zones to chain disentanglement crazing. (c) 2005 Elsevier Ltd. All rights reserved.