Platinum thin film resistance element and production method therefor

A gas sensor comprising a platinum thin film resistance element which includes:

• an insulating substrate having a smooth surface the unevenness of which is less than 1.1 .mu.m;
• a substantially pure platinum thin film formed as a continuous, solid film to a thickness of 100 to 1000 A on said surface of the insulating substrate, the resistance value of said thin film being stabilized by sputtering platinum particles forming said film onto said surface and by thereafter heat aging said film at temperatures from about 100.degree. C. to about 1000.degree. C. in a step-wise manner, said film having a kerf formed therein to increase its resistance value;
• a metal oxide semiconductor film formed on the platinum thin film to adsorb a gas to be sensed;
• and
• a pair of lead wires electrically connected to opposite end portions of the platinum thin film and fixed to the insulating substrate.