Chip on wafer on substrate structures and methods of forming are provided. The method includes attaching a first die and a second die to an interposer. The method also includes attaching a first substrate to a first surface of the first die and a first surface of the second die. The first substrate includes silicon. The first surface of the first side is opposite to the surface of the first die that is attached to the interposer, and the first surface of the second die is opposite to the surface of the second die that is attached to the interposer. The method includes bonding the interposer to a second substrate.