A high-frequency amplifier comprising: an input terminal for receiving a high frequency signal; a transistor for amplifying the high-frequency signal an output terminal for outputting an amplified high frequency signal; a first matching circuit connected between the input terminal and an input side of the transistor; and a second matching circuit connected between an output side of the transistor and the output terminal; wherein either the first matching circuit or the second matching circuit, or each of the first and the second matching circuit (4, 5) has a metal insulator metal, MIM, capacitor, the MIM capacitor has an upper electrode having one end connected to a connection point with a transmission line extending from the input terminal to an input side of the first matching circuit, from an output side of the first matching circuit to the input side of the transistor, from the output side of the transistor to an input side of the second matching circuit and from an output side of the second matching circuit to the output terminal, and a lower electrode having one end grounded through a source via, the upper electrode faces the lower electrode, the MIM capacitor is configured to achieve impedance matching of the fundamental wave of the high frequency signal with the transmission line and form a short-circuit point for a harmonic of the high frequency signal at the connection point with the transmission line, and wherein either a length of the upper electrode is a quarter of a wavelength of the harmonic, or the MIM capacitor includes a conductor having one end connected to another end of the upper electrode and a combined length of the upper electrode and the conductor is a quarter of a wavelength of the harmonic, or a length of the lower electrode is a quarter of a wavelength of the harmonic, or the MIM capacitor includes a conductor having one end connected to another end of the lower electrode and a combined length of the lower electrode and the conductor is a quarter of a wavelength of the harmonic. an input terminal for receiving a high frequency signal; a transistor for amplifying the high-frequency signal an output terminal for outputting an amplified high frequency signal; a first matching circuit connected between the input terminal and an input side of the transistor; and a second matching circuit connected between an output side of the transistor and the output terminal; wherein either the first matching circuit or the second matching circuit, or each of the first and the second matching circuit (4, 5) has a metal insulator metal, MIM, capacitor, the MIM capacitor has an upper electrode having one end connected to a connection point with a transmission line extending from the input terminal to an input side of the first matching circuit, from an output side of the first matching circuit to the input side of the transistor, from the output side of the transistor to an input side of the second matching circuit and from an output side of the second matching circuit to the output terminal, and a lower electrode having one end grounded through a source via, the upper electrode faces the lower electrode, the MIM capacitor is configured to achieve impedance matching of the fundamental wave of the high frequency signal with the transmission line and form a short-circuit point for a harmonic of the high frequency signal at the connection point with the transmission line, and wherein either a length of the upper electrode is a quarter of a wavelength of the harmonic, or the MIM capacitor includes a conductor having one end connected to another end of the upper electrode and a combined length of the upper electrode and the conductor is a quarter of a wavelength of the harmonic, or a length of the lower electrode is a quarter of a wavelength of the harmonic, or the MIM capacitor includes a conductor having one end connected to another end of the lower electrode and a combined length of the lower electrode and the conductor is a quarter of a wavelength of the harmonic.