Optomechanical resonators provide a route to interconversion of microwave and optical photons for quantum interconnects. We present a platform comprising a GaP photonic crystal cavity integrated on prefabricated niobium circuits, with mechanical modes at similar to 3.2 GHz and optomechanical coupling rates up to g0/2 pi similar or equal to 300 kHz. (C) 2022. The Author(s)