By connecting a grounding conductor pattern 11 directly to a grounding terminal 2 of a field-effect transistor 1 and connecting a series circuit comprising a stabilized resistor 12 and an open-circuit stub 13 having a length equal to quarter of a parallel resonance frequency, undesirable parallel resonance caused by the grounding conductor pattern 11 and the open-circuit stub 5 is suppressed, and a voltage drop in the stabilized resistor 3 is suppressed when a bias voltage is applied to the field-effect transistor 1. Accordingly, the operation of a microwave amplifier is stabilized. IMAGE
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