A layout of a common-base four-finger InGaAs/InP double heterostructure bipolar transistor (DHBT) has been designed and the corresponding DHBT has been fabricated successfully by using planarization technology. The area of each emitter finger was 1 x 15 mu m(2). The breakdown voltage was more than 7 V, the current could be more than 100 mA. The maximum output power can be more than 80 mW derived from the DC characteristics. The maximum oscillation frequency was as high as 305 GHz at I-c = 50 mA and V-CB = 1.5 V. The DHBT is thus promising for the medium power amplifier and voltage controlled oscillator (VCO) applications at W band and higher frequencies. (C) 2008 Elsevier Ltd. All rights reserved.