The burnable gases (methane, butane, coal gas and H-2) sensor based on the n + n combined structure semiconductor gas sensor is reported in this paper. The sensor is composed of two sensitive materials A and B whose conductive types are same. The materials A and B are all n-type materials. This sensor can obtain higher selectivity and better thermal stability than conventional sensors when the materials A and B satisfied certain conditions. Burnable gases sensors based on the n + n combined structure were fabricated and tested. The experimental results showed the sensors had higher selectivity and better thermal stability, and could be applied to monitor and control leakage of burnable gases.