A multi-layer high frequency device comprising a conductor and a dielectric layer, wherein the conductor comprises a metal selected from the group consisting of Cu, Au, Ag, and alloys thereof and at least part of the dielectric layer comprises a main component of calcium oxide, magnesium oxide, niobium oxide and titanium oxide represented by the formula:
- Ca{(Mg.sub. 1/3 Nb.sub. 2/3).sub.1-x Ti.sub.x }O.sub.3
- wherein 0<x<0.50, said main component being present within a range of 40 to 98 parts by weight;
- an accessory component comprising at least one element selected from the group consisting of SiO.sub.2 and B.sub.2 O.sub.3, said accessory component being present within a range of 2 to 60 parts by weight;
- and an additive comprising at least one oxide selected from the group consisting of MgO, NiO, CuO, MnO.sub.2 and WO.sub.3, said additive being present within a range of 0.1 to 10 parts by weight.