Gas sensor element and gas sensor

A gas sensor element comprising:

• a solid electrolyte body having oxygen ion conductivity, a measurement electrode provided on a first surface of the solid electrolyte body and exposed to a measurement gas, and a reference electrode provided on a second surface of the solid electrolyte body that is opposite to the first surface and exposed to a reference gas, wherein
• both the measurement electrode and the reference electrode comprise noble metal particles, solid electrolyte particles having oxygen ion conductivity, and pores, and
• the measurement electrode comprises:
• a surface measurement electrode layer comprising a surface serving as a contact surface with the measurement gas and an intermediate measurement electrode layer comprising a plurality of layers, one layer of the intermediate measurement electrode layer being disposed in contact with a surface at a solid electrolyte body side of the surface measurement electrode layer, and
• the surface measurement electrode layer has a higher porosity than porosity of each of the plurality of layers of the intermediate measurement electrode layer, and
• each of the plurality of layers included in the intermediate measurement electrode layer have a porosity increasing from the solid electrolyte body toward the surface measurement electrode layer.