Sensor element and gas sensor

A sensor element comprising:

• a long-length element main body including front and rear ends and one or more side surfaces, the front and rear ends being ends of the element main body in a longitudinal direction of the element main body, the one or more side surfaces being surfaces extending in the longitudinal direction;
• a detection unit including a plurality of electrodes disposed in the front end-side part of the element main body, the detecting unit detecting a specific gas concentration in a measurement-object gas;
• one or more connector electrodes disposed on the rear end-side part of any of the one or more side surfaces, the one or more connector electrodes used for electrical connection to outside of the sensor element;
• a porous layer that covers at least the front end-side part of the one or more side surface on which the one or more connector electrodes are disposed, the porous layer having a porosity of 10% or more;
• and
• a water-penetration reduction portion disposed on the one or more side surfaces so as to divide the porous layer in the longitudinal direction or to be located closer to the rear end than the porous layer, the water-penetration reduction portion being located closer to the front end than the one or more connector electrodes, a length (L) of the water-penetration reduction portion in the longitudinal direction being 0.5 mm or more, the water-penetration reduction portion including a dense layer covering the one or more side surfaces and having a porosity of less than 10% and a gap region in which the porous layer is absent, the gap region being arranged adjacent to the dense layer and at least the dense layer reducing capillarity of water in the longitudinal direction, and the dense layer and a portion of the porous layer located closer to the front end than the dense layer are adjacent to each other, or the dense layer and the portion of the porous layer are separated from each other with the gap region disposed in between.