Method of forming heterojunction bipolar transistor (HBT)

A method of forming an HBT structure includes forming an HBT epitaxial layer structure over a first substrate wafer; performing a first substrate transfer of the HBT epitaxial layer structure and the first substrate wafer onto a second substrate wafer, including inverting the HBT epitaxial layer structure and the first substrate wafer; removing the first substrate wafer; forming a first subcollector metal layer over the HBT epitaxial layer structure; performing a second substrate transfer of the subcollector metal layer and the HBT epitaxial layer structure onto a third substrate wafer with a second subcollector metal layer, including inverting the subcollector metal layer and the epitaxial layer structure; compression bonding the first and second subcollector metal layers to provide a bonded subcollector metal layer; and removing the second substrate wafer. The HBT structure includes the third substrate wafer, the bonded subcollector metal layer, and the HBT epitaxial layer structure.