Implantation of beryllium ions into a uniformly doped n-type InP epitaxial layer grown by vapour-phase epitaxy has been utilised to create a p+–n junction for flat-profile single-drift impatt diodes. An r.f. performance comparable to gallium arsenide has been obtained. A c.w. output power of 1.6 W with 11.1% conversion efficiency has been measured at 9.78 GHz and a peak power of 6.1 W with 13.7% efficiency has been measured at 10.8 GHz with 10% duty cycle. The f.m. noise of the c.w. oscillators is comparable to results reported for silicon.