According to one embodiment, a high-frequency semiconductor amplifier includes an input terminal, an input matching circuit, a high-frequency semiconductor amplifying element, an output matching circuit and an output terminal. The input terminal is inputted with a fundamental signal. The fundamental signal has a first frequency band and a first center frequency in the first frequency band. The input matching circuit includes an input end and an output end. The input end of the input matching circuit is connected to the input terminal. The high-frequency semiconductor amplifying element includes an input end and an output end. The input end of the high-frequency semiconductor amplifying element is connected to the output end of the input matching circuit. The high-frequency semiconductor amplifying element is configured to amplify the fundamental signal.