Fermi-level pinning (FLP) at metal/semiconductor interface, which is deviated from ideal Schottky-Mott limit, has been discussed for several decades based on various intrinsic and extrinsic models, and it has commonly been considered that the origin of FLP is ascribed only to semiconductor side. In this paper, we discuss FLP from the viewpoint of work function of met al. We focus on a fact that both of surface term of vacuum work function at metal/vacuum interface and intrinsic metal induced gap states (MIGS) at metal/semiconductor interface are described as a common physics of wave function tailing from met al. This suggests that the MIGS is regarded as a surface term of work function of metal at metal/semiconductor interface rather than interface states. Namely, the FLP caused by MIGS seems corresponded to modulation of work function. We also discuss how to control the work function modulation from both semiconductor and metal sides taking germanium as an example.