The characteristics of an interesting InGaP/AlXGa1-XAs/GaAs composite-emitter heterojunction bipolar transistor (CEHBT) are studied and demonstrated. By employing an AlXGa1-XAs graded layer between an InGaP emitter and GaAs base layer, a nearly zero conduction-band discontinuity can be obtained. Owing to the complete disappearance of the potential spike at the emitter/base hetero-interface, our CEHBT with AlXGa1-XAs graded layer exhibited good dc performance with current gains of 280 and 11 at collector currents of I-C = 12.6 mA and 0.2 nA, respectively. Furthermore, our CEHBT also shows a lower offset voltage and collector and base current ideality factors. In microwave characteristics, for a 3 x 20 mu m(2) device, the unit current gain cutoff frequency f(T) and maximum oscillation frequency f(max) are 41.3 and 35.4 GHz, respectively. Consequently, this work provides promise for high-performance analog, digital, and microwave device applications. (C) 2008 American Vacuum Society.