Two advances in InAs-based bipolar transistor technology are reported. Metamorphic InAs bipolar junction transistors (BJTs), grown on semi-insulating GaAs substrates, are reported for the first time, showing current gains comparable to similar structures grown homoepitaxially on InAs substrates. Measurements by atomic force microscopy report root-mean-square surface roughness as low as 0.661 nm, for a metamorphic BJT structure with a 5 pin thick InAs buffer. The quality of the epitaxial structure was investigated as a function of the buffer layer thickness, by measuring the reverse-leakage current density of metamorphic BJTs of 1, 2, and 5 pm InAs buffer layers, showing improved electrical characteristics with increasing buffer layer thickness. A second technological advance. is also. reported, concerning the development of a heterojunction bipolar transistor (HBT), with a strained, pseudomorphic InAs1-yPy ternary for the wide-gap emitter. The common emitter current gain of a control BJT device was measured at 110, and the HBT device, of identical doping structure achieved beta = 180. (C) 2002 Elsevier Science B.V. All rights reserved.