PURPOSE: To reduce the high frequency loss and to easily manufacture a waveguide input/output terminal type semiconductor integrated circuit high frequency device by simplifying the circuit constitution of the device.

CONSTITUTION: Metallic coupling pieces 4 and 5 are connected to high frequency input/output ends of a semiconductor integrated circuit chip 3 on which an ultrahigh frequency amplifier is mounted. High frequency signals inputted/ outputted from high frequency input/output ends are electromagnetically coupled to waveguides 1 and 2 as high frequency signal input/output terminals to an external circuit through metallic coupling pieces 4 and 5. Width L1 of a chip mounting part 6 is made narrower than width L2 of waveguides 1 and 2 to make the cut-off frequency of the waveguide mode higher than that of waveguides 1 and 2.