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Recently, we published a theoretical analysis of the nonlinear behavior of a MEMS variable capacitor, but until now these formulas where not confirmed with measurements. This paper shows for the first time a linearity measurement of a single MEMS varicap both as function of the frequency and as function of the bias voltage. The linearity is determined in a two-tone experiment in which two sinusoidal signals are applied to the device. The measurement is done on a series capacitor because it has a lower dynamic range requirement for the spectrum analyzer and the measurements can be done at a lower frequency than for the shunt configuration. However, at high frequency difference, the linearity becomes so high that it is difficult to measure due to the limitations of the measurement equipment. The measurement results confirm the mathematical analysis of. The linearity of a varicap decreases with increasing bias voltage and increases with increasing frequency difference between the two applied tones.