An InP/InGaAs single heterojunction bipolar transistor(SHBT) with high maximum oscillation frequency (f_(max)) and high cutoff frequency(f_t) is reported.Efforts have been made to maximize f_(max) and f_t simultaneously including optimizing the epitaxial structure,base-collector mesa over-etching and base surface preparation.The measured f_t and f_(max) both reached 185 GHz with an emitter size of 1×20μm~2,which is the highest f_(max) for SHBTs in mainland China.The device is suitable for ultra-high speed digital circuits and low power analog applications. An InP / InGaAs single heterojunction bipolar transistor (SHBT) with high maximum oscillation frequency (f_ (max)) and high cutoff frequency (f_t) is reported. Efforts have been made to maximize f_max and f_t simultaneously including optimizing the epitaxial structure , base-collector mesa over-etching and base surface preparation. The measured f_t and f_ (max) both reached 185 GHz with an emitter size of 1 × 20 μm ~ 2, which is the highest f_ (max) for SHBTs in mainland China. The device is suitable for ultra-high speed digital circuits and low power analog applications.