Method of fabricating a high frequency signal amplification device

A method for manufacturing a high-frequency signal amplification device comprising a dielectric multilayer substrate including a plurality of dielectric layers, and a semiconductor element with high-frequency signal amplification function mounted on the dielectric multilayer substrate;

• the method comprising steps of:
• preparing a dielectric multilayer substrate in which a plurality of metal conductors are formed on a surface of at least one of the plurality of dielectric layers, such that, in any range within a first region of a first surface of the dielectric multilayer substrate, proceeding from the surface of the dielectric multilayer substrate in a depth direction of the dielectric multilayer substrate, the plurality of metal conductors and a metal surface that is arranged at a position lower than the plurality of metal conductors is reached before reaching a second surface of the dielectric multilayer substrate;
• removing, with an agent capable of acting in a substantially vertical direction and removing dielectric materials more readily than metals, in the first region of the dielectric multilayer substrate, dielectric material from at least one of the plurality of dielectric layers, in a depth direction from the first surface of the dielectric multilayer substrate until reaching the metal conductors and the metal surface, so as to expose the metal conductors and the metal surface in the first region;
• and
• mounting the semiconductor element in the first region, such that a high-frequency signal is input into the semiconductor element via at least one of the plurality of metal conductors, and an amplified high-frequency signal is output from the semiconductor element via at least another one of the plurality of metal conductors.