A semiconductor device comprising: a substrate; a semiconductor element which includes a source electrode, a gate electrode and a drain electrode placed on a semiconductor substrate, said semiconductor substrate of the semiconductor element being placed on the substrate; a first peripheral circuit section which includes a first dielectric substrate and a second peripheral circuit section which includes a second dielectric substrate, the first peripheral circuit section and the second peripheral circuit section being respectively placed on the substrate, the first peripheral circuit section and the second peripheral circuit section being respectively placed adjacent to the semiconductor element; a via hole which passes through the first dielectric substrate from a top surface of the first dielectric substrate to a bottom surface of the first dielectric substrate; a first metal layer which is placed on an internal wall of the via hole; a second metal layer which is placed on the bottom surface of the first dielectric substrate which is facing with the substrate; and an electrode for grounding which is placed on the top surface of the first dielectric substrate, the source electrode being electrically connected to a single grounding path, said single grounding path consisting in a first wire, said electrode for grounding, said first metal layer and said second metal layer, whereby said first wire connects the source electrode to said electrode for grounding and whereby said first metal layer connects said electrode for grounding to said second metal layer, wherein the gate electrode is connected to a third metal layer placed on the top surface of the first dielectric substrate via a second wire, and the drain electrode is connected to a fourth metal layer placed on a top surface of the second dielectric substrate via a third wire, the top surface of the second dielectric substrate being opposite the bottom surface of said second dielectric substrate which is facing with the substrate, wherein the second metal layer is, in operation, at ground potential. a substrate; a semiconductor element which includes a source electrode, a gate electrode and a drain electrode placed on a semiconductor substrate, said semiconductor substrate of the semiconductor element being placed on the substrate; a first peripheral circuit section which includes a first dielectric substrate and a second peripheral circuit section which includes a second dielectric substrate, the first peripheral circuit section and the second peripheral circuit section being respectively placed on the substrate, the first peripheral circuit section and the second peripheral circuit section being respectively placed adjacent to the semiconductor element; a via hole which passes through the first dielectric substrate from a top surface of the first dielectric substrate to a bottom surface of the first dielectric substrate; a first metal layer which is placed on an internal wall of the via hole; a second metal layer which is placed on the bottom surface of the first dielectric substrate which is facing with the substrate; and an electrode for grounding which is placed on the top surface of the first dielectric substrate, the source electrode being electrically connected to a single grounding path, said single grounding path consisting in a first wire, said electrode for grounding, said first metal layer and said second metal layer, whereby said first wire connects the source electrode to said electrode for grounding and whereby said first metal layer connects said electrode for grounding to said second metal layer, wherein the gate electrode is connected to a third metal layer placed on the top surface of the first dielectric substrate via a second wire, and the drain electrode is connected to a fourth metal layer placed on a top surface of the second dielectric substrate via a third wire, the top surface of the second dielectric substrate being opposite the bottom surface of said second dielectric substrate which is facing with the substrate, wherein the second metal layer is, in operation, at ground potential.