In this study, a self-assembled diethyl vinylphosphonate (DVP) monolayer was grafted onto a germanium surface to investigate the modulation effect of self-assembled molecular monolayers on the Fermi level depinning on a germanium surface. Subsequently, the Fermi level depinning effect was comprehensively studied by analyzing the Schottky barrier height, uniformity, and stability. Experimental results demonstrated that DVP monolayers effectively alleviated the Fermi level pinning effect by forming a Schottky barrier of 0.50 eV on p-type germanium and reducing the Schottky barrier from 0.52 eV to 0.44 eV on n-type germanium. However, the depinning effect of the DVP monolayer resulted in a surface inhomogeneity of 12.2% among the samples of p-type germanium. We attributed this inhomogeneity to the incomplete passivation of the dangling bonds on the germanium surface. Furthermore, the Fermi level depinning effect of the DVP molecular monolayer degraded drastically after 48 h, which was attributed to the non-compact DVP monolayer caused by the complex chemical properties of the germanium surface.