Sensor element and gas sensor including the sensor

A plate-shaped sensor element extending in an axial direction, and comprising at least a first layer, a second layer and a third layer being stacked in a stacking direction, wherein

• the first layer and the third layer are mainly formed of ceramic,
• the second layer is disposed between the first layer and the third layer in the stacking direction,
• the second layer has an air introduction hole opened at a rear end surface thereof in the axial direction,
• the third layer is a heater layer which has a heating element inside thereof, and the heating element includes a heat generating portion at a front-end side of the sensor element in the axial direction, and
• in a cross-section perpendicular to the direction of the axis, a length L1 of a shortest line segment P1 connecting an upper end surface of the sensor element and the centroid G1 of the sensor element and a length L2 of a shortest line segment P2 connecting the upper end surface of the sensor element and the centroid G2 of the air introduction hole, satisfy a relationship of |L2−L1|/L1≤0.05.