This paper reviews recent progress in GaAs MESFETs and HBTs for high speed integrated circuits. SAINT MESFETs have succeeded in scaling down gate lengths to 0.1–0.15 μm and have realized propagation delay times of 5.9 ps gate −1. A multiplexer and demultiplexer operating at a high bit rate of 11.2 Gbit s −1 has also been developed. HBTs with ballistic collection transistor (BCT) structure have been proposed and have demonstrated highest speeds of 1.9 ps gate −1. High speed frequency dividers operating at 34.8 GHz have also been realized. Quantum interference transistors, which may provide innovations in future high performance devices, are also discussed.