InP/InGaAs heterojunction bipolar transistors (HBTs) with low-resistance Ti/Pt/Au contact directly on heavily doped InP emitter layer have been demonstrated. A specific contact resistance of Ti/Pt/Au to n-type InP with doping concentration of 2x10(19) cm(-3) was investigated with the tunneling model theoretically and transmission line model (TLM) experimentally, revealing that it depends greatly on the doping level. TLM measurements exhibited a low specific contact resistance of 3.5x10(-7) Omega cm(2), which can be applicable to the fabrication of HBTs. InP/InGaAs HBTs with n(+)-InP emitter layer have been demonstrated with excellent dc characteristics, including a low offset voltage of 0.12 V, a knee voltage of 0.5 V, and a current gain of 28. These results verify that the heavily doped InP emitter layer allows a low-resistance contact. (C) 2004 American Institute of Physics.