A new self-aligned emitter-base metallization (SAEBM) technique with wet etch is developed for high-speed heterojunction bipolar transistors (HBTs) by reducing extrinsic base resistance. After mesa etch of the base layer using a photo-resist mask, the base and emitter metals are evaporated simultaneously to reduce the emitter-base gap (S-EB) and base gap resistance (R-GAP). The InP/InGaAs/InP double heterojunction bipolar transistor (DHBT) fabricated using the technique has a reduced RGAP, from 16.48 Omega to 4.62 Omega comparing with the DHBT fabricated by conventional self-aligned base metallization (SABM) process. Furthermore, we adopt a novel collector undercut technique using selective etching nature of InP and InGaAs to reduce collector-base capacitance (C-CB). Due to the reduced R-GAP, the maximum oscillation frequency (f(max)) for a 0.5 mu m-emitter HBT is improved from 205 GHz to 295 GHz, while the cutoff frequency (f(T)) is maintained at around 300 GHz. (c) 2006 Elsevier Ltd. All rights reserved.