A direct growth approach using composite metamorphic buffers was employed for monolithic integration of InP-based high electron mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs) on Ge and Ge-on-insulator (GeOI)/Si substrates using molecular beam epitaxy. GaAs layers nucleated on these substrates and grown to a thickness of 0.5 μm were optimized to minimize the nucleation and propagation of antiphase boundaries and threading dislocations, and exhibited an atomic force microscopy rms roughness of ∼9 Å and x-ray full width at half maximum of ∼36 arc sec. A 1.1 μm thick graded InAlAs buffer was used to transition from the GaAs to InP lattice parameters. The density of threading dislocations at the upper interface of this InAlAs buffer was ∼107 cm-2 based on cross-sectional transmission electron microscopy analyses. HEMT structures grown metamorphically on GeOI/Si substrates using these buffer layers demonstrated transport properties equivalent to base line structures grown on InP substrates, with room temperature mobility greater than 10 000 cm2/V s. Similarly, double heterojunction bipolar transistors (D-HBTs) grown metamorphically on GeOI/Si substrates and fabricated into large area devices exhibited dc parameters close to reference D-HBTs grown on InP substrates.