We report excellent microwave performance demonstrated by metalorganic chemical vapor deposition (MOCVD) grown AlGaAs/GaAs HBT's with carbon-doped base. These devices achieve an ftof 76 GHz and an fmaxof 102 GHz. By varying device structures, current gain reaches over 300 in structures with a base doping of 2 × 1019cm-3. A static divide-by-4 divider implemented with C-doped base HBT's has been operated up to a frequency of 20.4 GHz. These results indicate the suitability of carbon doping for high-performance HBT's.