A tunable amplifier includes continuous tunability for both frequency and power levels. The tunable amplifier includes a combination of a tunable series resonator and a multi-stage LC network as the output matching network. The tunable amplifier incorporates a variable diode varactor with high breakdown voltage and high tuning range into a tunable resonator. The tunable resonator is connected to a fixed output matching network to enable a wide range of operating frequencies. The tunable amplifier enables high power, high efficiency, broadband and load-modulated power amplification, which is greatly desired for next-generation wireless communication systems and other high-frequency applications.