Capacitor mismatch is an important device parameter for precision analog applications. In the last ten years, the floating gate measurement technique has been widely used for its characterization. In this paper we describe the impact of leakage current on the technique. The leakage can come from, for example, thin gate oxide MOSFETs or high dielectric constant capacitors in advanced technologies. SPICE simulation, bench measurement, analytical model and numerical analyses are presented to illustrate the problem and key contributing factors. Criteria for accurate capacitor systematic and random mismatch characterization are developed, and practical methods of increasing measurement accuracy are discussed.