Patent ID: 7655123

Claim:
A gas sensor which has a diffusion regulating means for introduction of a gas to be measured, a first measuring chamber including a first pump cell comprising a first pair of pump electrodes, and a second measuring chamber including a second pump cell comprising a measuring electrode, wherein the gas to be measured is introduced into the first measuring chamber through the diffusion regulating means and a portion of the gas to be measured is introduced from the first measuring chamber into the second measuring chamber and is reduced or decomposed by the measuring electrode in the second measuring chamber, wherein the second pump cell measures the concentration of the gas to be measured on the basis of a pump current passing through the second pump cell, said gas sensor further comprising an electrode protective layer formed only on the surface of the measuring electrode of the second pump cell to cover the measuring electrode, said electrode protective layer comprising a porous alumina sintered body that includes alumina particles bonded together by a sintering adjuster bonding layer containing silicon dioxide and magnesium oxide so as to form communicating pores of 500-1100 Å in average pore diameter and 6-16% in porosity in said porous alumina sintered body.