Compound semiconductor amplifier and circuit module

A circuit module that stacks a high-frequency circuit board on which a compound semiconductor amplifier is mounted at an interval of ½ to one wavelength at a first frequency with respect to a wavelength in air,

• the compound semiconductor amplifier including:
• on an upper side of a semi-insulating substrate,
• a compound semiconductor;
• and an amplifier,
• wherein the semi-insulating substrate has a thickness for converting a wavelength at a first frequency into a second range of wavelength inside the semi-insulating substrate, and includes, on a lower surface, a metal layer having a sheet resistance value in a third range,
• the first frequency is a maximum frequency being used in the compound semiconductor amplifier,
• the second range of wavelength is 1/12 to ½ of the wavelength of the first frequency, and
• the third range is 3 to 1000 ohms.