PURPOSE: To selectively and well detect carbon monoxide even when periodic high temp. purge is performed by adding oxides of lead and lanthanum and palladium to a tin oxide semiconductor. ;CONSTITUTION: Aq. solns. of salts (e.g.; nitrate) of lead, lanthanum and palladium are prepared so that lead becomes 0.05-0.5mol%, lanthanum becomes 0.5-5mol% and palladium becomes 0.005-0.05mol% with respect to tin oxide to be independently infiltrated into sintered tin oxide or to be mixed to be infiltrated thereinto to form the responding part 3 of a semiconductor gas sensor 2. When lead and palladium are added to the tin oxide semiconductor, the selectivity of carbon monoxide (CO) to hydrocarbon such as methane or isobutane is enhanced and, when lanthanum is added thereto, the selectivity to hydrogen is also enhanced. Since CO selectivity can be ensured against obstruction gas to a certain degree not only within a temp. range of about 200-300°C being a CO detection temp. range but also within a temp. range of about 400°C capable of expecting purge effect at relatively high temp., CO can be detected stably over a long period of time.;COPYRIGHT: (C)1997,JPO
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