A new InP/InGaAs/InP DHBT structure with graded composition base was optimized and grown successfully in this work. The gallium (Ga) composition increased gradually from 47% on the collector side to 55% on the emitter side. The InP/InGaAs/InP DHBT structures were grown by gas source molecular beam epitaxy (GSMBE). Characteristics of InP, InGaAs and InGaAsP materials were investigated. High quality InP/InGaAs/InP DHBT structural materials were obtained. The InP/InGaAs/InP DHBT device with emitter area of 100 x 100 mu m(2) was fabricated. The offset voltage of 0.2 V. BV(CEO) > 1.2 V. current gain of beta=550 at V(CE) of 1.0 V were achieved. The reasons for the low breakdown voltage were analyzed. (C) 2011 Elsevier B.V. All rights reserved.