An example of such a coulometric sensor-actuator system is the combination of an ISFET pH sensor and a noble metal actuator at which H+ or OH--ions can be generated through the electrolysis of water. With the use of the small, planar, ICprocessed ISFET, a high degree of integration can be achieved by the deposition of a thin gold or platinum film electrode, closely spaced around the pH-sensitive gate of the ISFET. Figure 7 shows the basic elements of such a device.