Abstract: In fabricating an MFIC by mounting a semiconductor chip on a substrate having a microstrip line by MBB bonding, a benzocyclobutene (BCB) film is used as a dielectric film of the microstrip line. By providing a means for preventing the deformation, peeling, and cracking of the BCB film during the fabrication process, the thickness of the dielectric film is held substantially equal even after flip-chip mounting, which reduces impedance fluctuations.

Abstract: A channel layer of n-type GaAs doped with Si as an impurity is formed on a GaAs semiinsulating substrate. A gate electrode of, for example, aluminum is formed on the channel layer. The gate electrode is in Schottky-contact with channel layer. Formed on opposite sides of the gate electrode on the channel layer are drain- and source side electric field relaxation layers of n-type In.sub.x G.sub.1-x As doped with impurities. Each electric field relaxation layer substantially produces a potential difference at its lateral edge portion by an electric current flowing across the lateral edge portion. A WSi drain electrode is formed on the drain-side electric field relaxation layer. A WSi source electrode is formed on the source-side electric field relaxation layer.