Metallic Oxide Semiconductor Field Effecttransistor (MOSFET) array compound type gas chemical microsensor has been developed. The device consists of three MOSFETs, a heating resistor and a diode used as temperature sensor. Two of the MOSFETs have their gates covered with thin catalytic and sensitive materials: Palladium (Pd) and Yttria-Stabilized Zirconia (YSZ) and act as hydrogen and oxygen sensitive units respectively. The third MOSFET has a standard gate covered with aluminium and acts as a reference. This paper discusses the structure, working principle and fabrication process of the device. In addition, some relevant experimental curves are presented. Analysis of characteristics of the device, such as sensitivity, stability, selectivity, temperature property and time response, has been performed. Obtained results show that the exposure to different gases causes the change of threshold voltage of each gas sensitive MOSFET. They also exhibit excellent characteristics of the device.