A highly reliable ceramics substrate which can sufficiently secure a bonding strength of a surface conductor in an initial state and after a lapse of time (e.g., after a PCT) is provided. The multilayer ceramics substrate has a surface conductor on at least one surface of a multilayer body constituted by a plurality of laminated ceramics substrate layers. A reaction phase formed by a reaction between a ceramics component in the ceramics substrate layers and a glass component in the surface conductor is deposited at an interface between the surface conductor and ceramics substrate layers. For example, an alumina filler in the ceramics substrate layers and Zn in the surface conductor react with each other, thereby forming ZnAl2O4 as the reaction phase.