The aim of this paper is to present a new approach which consists to correlate or coupled the functional and electrical stress with temperature. This approach can be extremely useful in the predicting the stressing effect and the impact of IXGH-IGBT I-V characteristics on circuit degradation. Moreover, this new approach significantly improves such parameters likes (threshold voltage Vth, collector saturation current, the stress and enhanced collector leakage current) and provides new capability for use this power device IXGH-IGBT in an actual circuit environment and modules. We also explain the physical reasons behind the improvement obtained using functional electrical stress on the IGBTs for IXYS constructor with temperature. Moreover, the forward blocking capability of IXGH-IGBT under a coupled Functional - Electro stress at high temperature was analyzed using simulation. This paper gives a straight comparison in term of the stress for improving the switching speed of IGBT device. This study is essential to ensure product reliability and to the evaluation of hot carrier reliability in the early stages. Furthermore, our reliability study permits us to improve the implantation of the device in a circuit, as well as its use in industrial operating conditions. The need for good simulator (Spice, Spice) to carry out a reliability study is pointed out in this paper.