PURPOSE: To obtain a semiconductor-type ammonia gas sensor which is highly sensitive to ammonia gas and which is provided with selectivity with reference to flammable gases including an organic solvent in a metal-oxide semiconductor- type gas sensor, of a conventional type, which is composed mainly of a palladium-added tin oxide semiconductor and to obtain the manufacturing method of a sensor provided with such characteristics.

CONSTITUTION: A metal-oxide semiconductor part 5 is constituted so as to be provided with a palladium-rich surface layer 6 in which the atomic fraction of palladium and tin (Pd/Sn×100) is added to 4 to 20% by an electrodeposition method, an immersion method or the like and with a metal-oxide semiconductor inner part 7 in which the concentration of palladium to be added is adjusted to 1/20 to 1/4 with reference to the concentration of the palladium in the palladium-rich surface layer 6.