Sensor element and gas sensor

A sensor element configured to detect a specific gas concentration in a measurement-object gas, the sensor element comprising:

• an element body with an oxygen-ion-conductive solid electrolyte layer and a measurement-object gas flow section located inside the element body that introduces and flows the measurement-object gas;
• a reference electrode disposed inside the element body;
• a measurement-object gas side electrode disposed on a portion of the element body that is exposed to the measurement-object gas;
• a first conducting section including a reference electrode terminal disposed on an outside of the element body, and a reference electrode lead that is electrically continuous between the reference electrode terminal and the reference electrode;
• and
• a lead insulation layer covering a portion of the reference electrode lead that is located inside the element body,
• wherein the reference electrode lead is configured to flow a reference gas, which serves as a reference for detecting the specific gas concentration in the measurement-object gas, to the reference electrode, and
• a region of 50% or more, from an end on the reference electrode side, of the total area of the lead insulation layer in a planar view is configured as a dense region with a porosity of 5% or less.