Abstract Excellent device performance at both d.c. and microwave frequencies has recently been obtained from GaAs based devices grown on Si substrates. In GaAs MESFETs on Si, current gain cutoff frequencies and maximum oscillation frequencies of f T = 13.3 GHz and f max = 30 GHz have been obtained for 1.2 μm devices, which is nearly identical to the performance achieved in GaAs on GaAs technology for both direct implant and epitaxial technology. For heterojunction bipolar transistors, current gain cutoff frequencies and maximum oscillation frequencies of f T = 30 GHz and f max = 11.3 GHz have been obtained for emitter dimensions of 4 × 20 μm 2. These results compare with the best reported HBT on GaAs substrates of f T = 40 GHz and f max = 26 GHz with much smaller geometry. Given the performance already demonstrated in AaAs on Si devices and the advantages afforded by this technology, the growth of III–Vs on Si promises to play an important role in the future of heterojunction electronics.