GAS SENSOR

PROBLEM TO BE SOLVED: To provide a p-n junction diode-type gas sensor whose sensor constitution is simple, in which the aged deterioration of a diode characteristic in a long-term use is small and which can detect the gas concentration of molecules comprising hydrogen atoms such as H2, NH3, H2S, hydrocarbon or the like contained in a gas to be detected. SOLUTION: A p-n junction in which a first semiconductor layer and a second semiconductor layer of respectively different conductivity types are brought into contact is formed. Ohmic electrodes are formed on surfaces of the semiconductor layers. A catalyst layer containing a metal catalyst component which dissociates the hydrogen atoms from the molecules comprising the hydrogen atoms is formed on one electrode among the ohmic electrodes.