An analysis of the shallow trench isolation (STI) edge effect on CMOS Schottky barrier diode (SBD) is reported in this article. The STI edge effect, which includes the impact of the fringing electric field and the nonplanar intersection of STI, significantly distorts the performance of SBDs with a small junction. Due to this effect, when an array SBD is formed by connecting several SBDs with a small junction in parallel, the series resistance of the array SBD is not reduced as expected. Therefore, the cut-off frequency of an array SBD with a small unit junction SBD degenerates quickly. This phenomenon is observed in measurements of fabricated CMOS SBD prototypes.