Patent ID: 8721857

Claim:
A gas sensor element having a main body that comprises: a solid electrolyte body having oxygen ion conductivity; a measurement gas-side electrode and a reference gas-side electrode that are respectively provided on an opposite pair of first-side and second-side surfaces of the solid electrolyte body; a porous diffusion-resistant layer laminated on the first side of the solid electrolyte body so that a measurement gas passes through the diffusion-resistant layer to make contact with the measurement gas-side electrode; and a heater layer which is laminated on the second side of the solid electrolyte body and includes a heater that generates heat upon being supplied with electric power, wherein the main body is substantially quadrangular in shape to have, a pair of plane portions that are opposite to each other in a lamination direction of the main body, a pair of plane portions that are opposite to each other in a direction perpendicular to the lamination direction, and four corner portions formed between the four plane portions, the four corner portions include a pair of diffusion-side corner portions that are located on the first side of the solid electrolyte body and each have formed therein a measurement gas inlet of the diffusion-resistant layer via which the measurement gas is introduced to the diffusion-resistant layer, on the main body, there are provided a protective layer which is comprised of a first protective layer that covers, among the four corner portions, at least the pair of diffusion-side corner portions and a second protective layer that covers an entire outer periphery of the main body including the first protective layer, and the protective layer has a larger thickness at the diffusion-side corner portions than at the an average thickness for each of the plane portions of the main body.