Chemical and electrochemical sensors and sensor arrays can be produced using microfabrication and micromachining technologies. These technologies permit the formation of three-dimensional structures and also produce geometrically well-defined, highly reproducible sensor prototypes. Most present chemical and electrochemical sensors operate using a single device for absolute measurements. There are many circumstances in which interference by other species, the signal-to-noise ratio, and/or the selectivity and sensitivity are less than desirable when using a single sensor. It is feasible to employ a differential mode of sensor operation to overcome these weaknesses. In the differential mode of measurement, a pair of identical sensors is used, with one sensor as the active device, and the other serving as a reference. The active device may incorporate an electrocatalyst, while the reference sensor does not. The difference in these two sensor outputs can quantify the sensing species present. The advantages and practicality of the differential mode of sensor operation can be realized only if the manufacture of identical sensor-pair structures can be accomplished relatively simply and at modest cost. Microfabrication and micromachining technologies provide an excellent means to produce two-sensor arrays of well-defined identical structures at a reasonable manufacturing cost. This presentation describes the design, processing and experimental results of some of these differential mode two-sensor arrays. The advantages and the potential applications of these sensors will also be discussed.