Co-fabrication of a radio-frequency (RF) semiconductor device with a three-dimensional semiconductor device includes providing a starting three-dimensional semiconductor structure, the starting structure including a bulk silicon semiconductor substrate, raised semiconductor structure(s) coupled to the substrate and surrounded by a layer of isolation material. Span(s) of the layer of isolation material between adjacent raised structures are recessed, and a layer of epitaxial semiconductor material is created over the recessed span(s) of isolation material over which another layer of isolation material is created. The RF device(s) are fabricated on the layer of isolation material above the epitaxial material, which creates a local silicon-on-insulator, while the three-dimensional semiconductor device(s) can be fabricated on the raised structure(s).