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HBTs are used in Gb/s fiber-optic ICs, GHz analog-digital converters, and microwave PLLs. To permit clock rates exceeding 100 GHz, transistors with several hundred GHz bandwidth are required. The interconnects must have small inductance and capacitance per unit length, and the transistor spacings must be small to minimize wire lengths. Given that fast HBTs operate at /spl sim/10/sup 5/ A/cm/sup 2/, efficient heat sinking is then vital. We report here a transferred-substrate HBT IC technology with record HBT power-gain cutoff frequency (f/sub max/). The interconnects, microstrip on Benzocyclobutene (BCB), have a low (/spl epsiv//sub r/=2.7) dielectric constant for low capacitance and a ground plane for low ground-return inductance. Transistor heatsinking is provided by electroplated gold thermal vias.