For the first time, an insulated gate bipolar transistor with a novel buffer, called injection efficiency tuning IGBT (IET-IGBT), is proposed and verified by two-dimensional (2D) mixed device-circuit simulations. The structure of the proposed device is almost identical with that of the conventional IGBT, except for the buffer layer which is formed by employing a very highly doped stripped n(+) and a weakly doped n(-) structure. Compared with the conventional PT-IGBT and recent FS-IGBT, the proposed device exhibits a better trade-off relation between the conduction and switching losses. An interesting feature of the IET-IGBT is that its on-resistance can be largely decreased at the expenditure of a moderate and neglectable increase in the turn-off time. The weakly doped n(-) buffer region leads to a high injection efficiency anode providing an optimum level of conductivity modulation required for a given on-state voltage drop in the n-drift region, while the very highly doped n(+) buffer region results in a low injection anode accelerating the device turn-off. Detailed physical mechanisms are given. (c) 2006 Elsevier Ltd. All rights reserved.