A divide-by-four frequency divider using AIGaAs/GaAs HBTs with GalnAs/GaAs emitter cap layers was designed and fabricated. A maximum toggle frequency of 22.15 GHz was obtained at a power supply voltage of 9 V and a total power dissipation of 712 mW. The minimum input signal power was under 0dBm and the free-running frequency was as high as 20 GHz.