is around 1 4 m 1400 nm and that the bottom of the opening is at 600 nm from the surface the thickness of region 125 can be around 60 nm the total thickness of region 114 under the bottom of the opening can be around 120 nm the thickness of the epitaxial layer free of overdoping can be around 200 nm and the thickness of the adapted doping collector region 130 can be around 200 nm an essential characteristic of the present invention is to provide an opening of non negligible depth in epitaxial layer 101 and to provide several levels of base doping around and at the bottom of this opening thus the doping level of intrinsic base region 114 can be set as desired and the resistance of the extrinsic base including regions 115 and 117 towards base contact region 112 can be adjusted as desired to optimize the base resistance to reduce the base emitter and base collector capacitances and to improve the reverse characteristics of the emitter base junction indeed these base emitter and base collector capacitances essentially depend on the distance between the more doped part 112 and emitter region 114 on the one hand and the more doped regions of collector 130 on the other hand the depth of the opening and the base doping levels can be adjusted according to the desired results of course the present invention is likely to have various alterations modifications and improvements which will readily occur to those skilled in the art in particular the base contact emitter contact and collector contact recoveries have not been described but can.