Hysteresis is a very important parameter in microsensors that must be characterized; however, few previous studies have performed the necessary investigations. Low-hysteresis voltages indicate a reliable and repeatable microsensor response. Figure 9 presents a hysteresis characterization of the fabricated EGFET-based microsensor. The hysteresis voltages were measured using a standard testing solution with concentration altered every 20 m in the sequence of 2.5, 5, 25, 50, 25, 5, 2.5, 0.5, 0.25, 0.5, and 2.5 mM. A very small hysteresis voltage (7.5 mV) was measured at 2.5 mM.