Semiconductor devices and methods of forming the semiconductor devices are described herein. A method includes providing a first material layer between a second material layer and a semiconductor substrate and forming a first waveguide in the second material layer. The method also includes forming a photonic die over the first waveguide and forming a first cavity in the semiconductor substrate and exposing the first layer. Once formed, the first cavity is filled with a first backfill material adjacent the first layer. The methods also include electrically coupling an electronic die to the photonic die. Some methods include packaging the semiconductor device in a packaged assembly.