Abstract: A sensor element includes an element body, a detection unit, a connector electrode, a porous layer that covers at least the front end-side part of a side surface on which the connector electrode is disposed and that has a porosity of 10% or more, and a dense layer. The dense layer is disposed on the side surface so as to divide the porous layer in the longitudinal direction of the element body or to be located closer to the rear end than the porous layer. The dense layer is located closer to the front end of the sensor element than the connector electrode. The dense layer covers the side surface and has a porosity of less than 10%. The dense layer includes an overlap portion that is a front end portion of the dense layer and covers the outer surface of a part of the porous layer.

Abstract: A sensor element includes an element body, an upper connector electrode disposed on a first surface of the element body, and a protective layer that covers at least a front end-side part of the first surface. The protective layer includes a first specific protective layer having a thickness T1 of 10 ?m or less. The ratio T1/T2 of the thickness T1 to the thickness T2 of a front-side portion of the protective layer which faces the front end of the first specific protective layer is 1.0 or less.