Compound semiconductor integrated circuit

A compound semiconductor integrated circuit, comprising:

• a substrate;
• at least one compound semiconductor electronic device formed on said substrate;
• a first metal layer containing Au formed on said compound semiconductor electronic device, and at least partly electrically connected to said compound semiconductor electronic device;
• a protection layer covering said compound semiconductor electronic device and at least part of said first metal layer;
• a plurality of second metal layers, each including at least a Cu layer, formed on said protection layer, at least two of said plurality of second metal layers stacked vertically and overlapped with each other, and at least one of said plurality of second metal layers partly electrically connected to said first metal layer;
• and
• at least one dielectric layer separating each pair of adjacent second metal layers stacked vertically,
• wherein said protection layer is made of SiN, and all of metal layers composed mainly of Cu on the same side of said substrate that said at least one compound semiconductor electronic device is formed are formed above said protection layer.