PURPOSE: To reduce wiring capacitance, and to propagate an ultra-high speed signal by composing insulators among wirings of air and forming the number of wiring layers in multilayers.

CONSTITUTION: An inorganic insulating material consisting of SiO2 is shaped onto the whole surface on a substrate 1, a first-layer wiring support member 6 is formed at a specified position according to a pattern, a first-layer inter-layer insulating layer 7 is applied onto the substrate 1, and a first-layer through-hole 8 section between wiring layers and the upper section of the first-layer wiring support member 6 are developed and removed and the whole is post-baked. A thin-film composed of copper is shaped onto the first-layer inter-layer insulating layer 7, a first layer wiring 9 is formed, a second-layer wiring support member 10 and a second layer inter-layer insulating layer 11 are shaped onto the first layer wiring 9, and a second-layer through-hole 12 and the upper section of the second-layer wiring support member 10 are gotten rid of through etching. A second layer wiring 13 is formed onto the second-layer inter-layer insulating layer 11, and these each process is repeated and wirings up to a fourth layer wiring 19 from a third layer wiring 16 are shaped. Lastly, respective inter-layer insulating layer 7, 11, 15, 18 is taken off, and air gap wirings utilizing air gaps 20 are formed. Accordingly, an ultra-high speed signal can be propagated.