In this paper, an investigation of the impact of negative gate voltage (VG(off)) on the turn-off performance of Si-IGBT device is described. In general, the switching energies of the IGBT devices are given at specific VG(off) = -15 V. When estimating power dissipation of the inverter system at different VG(off), a correction factor of the switching energies from the given values is required. Although it has been known that the value of VG(off) affects the turn-off switching characteristic, it has not been investigated in detail. Hence the correction factor for the turn-off energy (Eoff) at different VG(off) and gate resistance (RG) conditions is difficult to estimate theoretically. The effect of VGE(off) on the behavior of collector-emitter voltage (VCE) during turn-off operation of the IGBT is investigated. The estimation method of Eoff at different VG(off) and RG conditions is derived from the investigation and the theoretical formula confirmed by experimental results. Then, a novel procedure to estimate the Eoff correction factor at different gate drive condition is proposed.