An integrated circuit technology combines heterojunction bipolar transistors (HBTs), high electron mobility transistors (HEMTs) and other components along with interconnect metallization on a single substrate. In a preferred embodiment a flat substrate is patterned, using dry etching, to provide one or more mesas in locations which will eventually support HEMTs. A device stack including HEMT and HBT layers is built up over the substrate by molecular beam epitaxy, with the active HEMT devices located on the mesas within openings in the HBT layer. In this way the active HEMT is aligned with the HBT layer to planarize the finished integrated circuit.