(AlGa)As–GaAs npn bipolar transistors have been analyzed for application to high speed digital integrated circuits. Projected propagation delays of 10 ps and associated speed x power products of 30 fJ make this an attractive high speed technology. Discrete (AlGa)As–GaAs npn bipolar transistors have been fabricated on n+ GaAs substrates. The epitaxial structures have been grown by MBE to produce very thin, highly doped base layers. Current gains up to 190 have been measured. Microwave measurements on packaged devices yield a value of fτ=11 GHz. This value is limited by package parasitics. Modeling the entire packaged device yields a value Of fτ=34 GHz for the intrinsic HBT. This level of performance should be realizable in ICs and affirm the potential of this technology for ultra-high speed ICs.