The crystallization of As_xSe_1−x from the glassy state (0.005<x<0.03) is analyzed from calorimetric investigations. For each composition, the apparent activation energy for the crystallization reaction is determined with the Kissinger method. Upon increasing x, the apparent activation energy decreases. It is also found that the dependence of the inverse of the apparent activation energy for crystallization falls linearly with the reciprocal of the mean temperature used in the experiment. The latter result unambiguously indicates that the crystallization process for As_xSe_1−x, in the composition range investigated, is mainly controlled by the viscosity of the medium. Therefore, the crystallization reaction totally disappears when the amount of As atoms in the alloys reaches such a value capable of connecting enough Se chains to block their movement.