In this work we have investigated the seasoning effect in SET state occurring during cycling of multi-megabit Phase Change Memory arrays. The impact of the erasing waveform on this phenomenon has been experimentally evaluated. The physical nature of the phenomenon has been discussed in relation to the electro-thermal characteristics of the active material. The study of such phenomenon is also important to comprehend the transition dynamics of the GST material towards its crystalline state and to develop accurate models allowing an estimate of the PCM cells behavior as a function of the operative cycles. (C) 2010 Elsevier Ltd. All rights reserved.