A ceramic substrate of the present disclosure is a ceramic substrate including a ceramic body having a ceramic layer on a surface thereof and a surface electrode placed on a primary face of the ceramic body. Between the surface electrode and the ceramic layer is an oxide layer made of an insulating oxide having a melting point higher than the firing temperature for the ceramic layer. The oxide layer also extends on the ceramic layer not occupied by the surface electrode. The oxide layer on the ceramic layer not occupied by the surface electrode has a rough surface.