Integrated 3D circuit package with a window interposer

3D integrated circuit packages with window interposers and method to form such a semiconductor package will be described. For example, a semiconductor package includes a substrate. A top semiconductor die is disposed over the substrate. An interposer having a window is disposed between the substrate and the top semiconductor die and connected thereto. A bottom semiconductor die is disposed in the window of the interposer and connected to the upper semiconductor die. In another example, a semiconductor package includes a substrate. A top semiconductor die is disposed over the substrate. An interposer is disposed between the substrate and the top semiconductor die and connected thereto. A bottom semiconductor die is disposed in a same area as the interposer and connected to the upper semiconductor die.