In the design of an emitter of power transistors, the main problem is to attain good current amplification factor β for a given injection level. At a higher injection level, the current amplification factor drops off as the emitter current density is increased. One of the commonly used methods to reduce this fall-off is by increasing the emitter area. On account of the socalled "base region self-crowding effect", this would make the emitter current density not uniform over the emitter junction area, the current density dropping off rapidly at regions far from the base contact. In this paper, this effect is analyzed quantitatively for nearly all injection levels both for circular and comb structures of the junction. An "exponential decay" for the emitter current density distribution, and an effective emitter area are obtained. These results may give some reference for the design of power transistors.