Abstract: Disclosed is a method for fabricating very high performance semiconductor devices, particularly bipolar-type transistors having a heavily doped inactive base and a lightly doped narrow active base formed by ion implantation. In order to prevent the high dose boron implantation, for an NPN transistor, from getting into the active base region, a self-aligned mask covering the emitter contact i.e., active base region, is required for inactive base implantation. The self-aligned mask is anodically oxidized aluminum pads. The device wafer metallized with blanket aluminum film is immersed in a dilute H.sub.2 SO.sub.4 solution electrolytic cell which selectively anodizes only the aluminum lands situated over the Si.sub.3 N.sub.4 /SiO.sub.2 defined device contact windows. The aluminum oxide formed by anodization process is porous but may be sealed and densified. The aluminum film that is not anodized is then selectively etched off using either chemical solution or sputter etching.