Since the first SiGe HBTs reported in the late eighties  many groups were involved in the development of these devices [2,3,4]. Transit frequencies of 116 GHz  and 130 GHz , and maximum oscillation frequencies of 160 GHz [7,8] were reported. The devices are fully compatible with the existing state-of-the-art 0.18 m CMOS technology [9,10]. Digital application-specific integrated circuits (ASICs) are combined with SiGe HBT circuits in the so-called SiGe BICMOS technology and are in volume production . The SiGe HBT is considered an essential technology for over 10 Gb/s optical communication systems [12,13]. However, a shortcome of Si-based HBTs is their comparatively lower breakdown voltage.