Metamorphic heterojunction bipolar transistor (M-HBT) structures and metamorphic P-I-N (M-PIN) photodiode structures were grown on GaAs substrates. A compositionally graded AlGaInAs buffer layer was used to expand the lattice constant to that of InP. Cross-sectional transmission electron micrographs of the M-HBT structure showed that the dislocations from compositional grading were predominantly localized in the buffer layer and that the device layers possessed planar interfaces. Secondary ion mass spectroscopy depth profiles of the 4 X 10(19) cm(-3) beryllium-doped In0.53Ga0.47As base layer exhibited sharp doping interfaces, indicating that metamorphic growth was not causing enhanced beryllium diffusion. The current gain of large emitter M-HBT devices approached the current gain for the same device structure grown on an InP substrate. A P-I-N photodiode structure was also grown metamorphically on a GaAs substrate and lattice matched on an InP substrate. Both types of photodiodes showed almost identical responsivities and bandwidths. A responsivity to 1.55 mum radiation of 0.55 A/W. which corresponds to an external quantum efficiency of 44%, was obtained with M-PIN photodiodes. The 3 dB bandwidths exceeded 20 GHz for M-PIN photodiodes with diameters of 25 mum or smaller. These results are very encouraging for the application of metamorphic technology to nonmajority carrier devices.