Phase transition between non-extremal and extremal Reissner-Nordstr\"om black holes

We discuss the phase transition between non-extremal and extremal Reissner-Nordstr"om black holes. This transition is considered as the $T\to 0$ limit of the transition between the non-extremal and near-extremal black holes. We show that an evaporating process from non-extremal black hole to extremal one is possible to occur, but its reverse process is not possible to occur because of the presence of the maximum temperature. Furthermore, it is shown that the Hawking-Page phase transition between small and large black holes unlikely occurs in the AdS Reissner-Nordstr"om black holes.