This letter investigates the extraction of activation energy for the crystallization of an amorphous chalcogenide material in phase-change memories. It is demonstrated for the first time that the critical resistance, which is the value of resistance defining the crystallization time for the chalcogenide material, has a major impact on the extraction of the activation energy for crystallization. Applying a statistical Monte Carlo model for crystallization coupled with an electrothermal model for both the amorphous and crystalline phases, we analyzed the standard methodology for the extraction of the activation energy. It is shown that a careful choice of the critical resistance is mandatory and a new accurate technique is proposed, resulting in a reliable value for the crystallization activation energy of 2.6 eV in the Ge 2 Sb 2 Te 2 -based devices.