A method of fabricating a semiconductor structure includes providing an engineered substrate including a polycrystalline substrate, a barrier layer encapsulating the polycrystalline substrate, and a bonding layer coupled to the barrier layer. The method further includes forming a first silicon layer coupled to the bonding layer, forming a dielectric layer coupled to the first silicon layer, forming a second silicon layer coupled to the dielectric layer, removing a portion of the second silicon layer and a corresponding portion of the dielectric layer to expose a portion of the first silicon layer, forming a gallium nitride (GaN) layer coupled to the exposed portion of the first silicon layer, forming a gallium nitride (GaN) based device coupled to the GaN layer, and forming a silicon-based device coupled to a remaining portion of the second silicon layer.