Recent progress in integrating ferroelectrics directly on silicon opens the exciting possibility of implementing ferroelectric-semiconductor devices. One of the major problems for such integration is the instability of the ferroelectric state in very thin films, which is mainly controlled by the screening ability of the ferroelectric-semiconductor interface. We show here that the presence of built-in potential in the semiconductor can strongly influence the screening ability of the interface. The built-in potential depends on the electron affinities and surface states density and can be controlled by choosing the materials carefully.