Recent progress in integrating ferroelectrics directly on silicon opens the exciting possibility of implementing ferroelectric-semiconductor devices [1]. 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 difference in ferroelectric-semiconductor work function can strongly influence the screening ability of the interface. The work function difference can be controlled by choosing the materials carefully.