A method for integrating III-V semiconductor materials onto a rigid host substrate deposits a thin layer of reactive metal film on the rigid host substrate. The layer can also include a separation layer of unreactive metal or dielectric, and can be patterned. The unreactive metal pattern can create self-aligned device contacts after bonding is completed. The III-V semiconductor material is brought into contact with the thin layer of reactive metal. Bonding is by a low temperature heat treatment under a compressive pressure. The reactive metal and the functional semiconductor material are selected to undergo solid state reaction and form a stable alloy under the low temperature heat treatment without degrading the III-V material. A semiconductor device of the invention includes a functional III-V layer bonded to a rigid substrate via an alloy of a component of the functional III-V layer and a metal that bonds to the rigid substrate.