Sensor element and gas sensor

A sensor element for detecting a specific gas concentration in a measurement-object gas, the sensor element comprising:

• an element body including an oxygen-ion-conductive solid electrolyte layer, the element body having a longitudinal direction;
• a measurement electrode disposed in the element body so as to come into contact with the measurement-object gas;
• a reference electrode disposed in the element body so as to come into contact with a reference gas, the reference gas being used as a reference to detect the specific gas concentration in the measurement-object gas;
• and
• a heater disposed in the element body and configured to heat the solid electrolyte layer, wherein
• a center of gravity of the reference electrode overlaps the measurement electrode as viewed in a thickness direction of the solid electrolyte layer,
• a length of each of the reference electrode and the measurement electrode in a front-rear direction is less than or equal to 1.1 mm, the front-rear direction being a direction along the longitudinal direction of the element body, and
• an area of the reference electrode as viewed in the thickness direction is greater than or equal to 1.0 mm2.