µ-3/an InGaAsP lasers with 3dB bandwidths of 24 GHz and intrinsic resonance frequencies in excess of 22 GHz have been successfully fabricated. This is the highest bandwidth ever reported for a semiconductor laser, and the highest resonant frequency for InGaAsP lasers. Excellent modulation efficiencies are observed to high frequencies. © 1990, The Institution of Electrical Engineers. All rights reserved.