Patent ID: 7276745

Claim:
A gas sensor comprising: a gas sensing portion formed by a metal-oxide semiconductor portion whose electrical characteristic varies according to a gas to be detected and a catalytic portion dispersed on a surface of the metal-oxide semiconductor portion; and an insulating portion formed on a surface of the gas sensing portion so that a part of the gas sensing portion may be exposed; wherein the metal-oxide semiconductor portion is comprised mainly of SnO 2 , the catalytic portion is comprised of a noble metal M and the insulating portion is comprised mainly of SiO 2 , wherein a first surface additive rate, which is expressed by Si/(M+Si) representing the ratio in the number of atoms of Si to M, of the gas sensing portion having the insulating portion is determined to be 65% or more to 97% or less, and a second surface additive rate, which is expressed by Si/(Sn+Si) representing the ratio in the number of atoms of Si to Sn, of the gas sensing portion is determined to be 75% or more to 97% or less, wherein said first surface additive rate and said second surface additive rate is obtained by the number of atoms measured by X-ray photoelectron spectroscopy (XPS) at a detection depth in the range of 4-5 nm at a 45 degree extraction angle in a detection area of 100 μm.