High frequency semiconductor device

A high frequency semiconductor device comprising:

• a semiconductor substrate;
• a ground plate connected to the ground potential and provided substantially over all a surface of the semiconductor substrate;
• a power-supply conductor provided above said ground plate, with an insulating layer provided therebetween, said power-supply conductor being connected to a power-supply potential;
• a throughhole piercing through the ground plate for connecting the power-supply conductor to an active region formed in the semiconductor substrate through the throughhole;
• and
• a line conductor provided above said ground plate, with an insulating interlayer provided therebetween;
• wherein:
• said line conductor combines with said ground plate or said power-supply conductor to form a high frequency transmission line;
• and
• the capacitance between said line conductor and one of said ground plate and said power-supply conductor is smaller than the capacitance between said ground plate and said power-supply conductor.