Abstract: A method of integrating impedance matching with power combining is introduced. A broadband, high power, high power-density chip amplifier in S-band is successfully developed by four GaN HEMT power chips. Prematching is used for increasing the input impedances of chips. Chebyshev impedance-matching is applied for broadband matching. Isolating resistor is optimized to increase the isolation between combining branches, therefore the circuits stability is improved. The amplifier is tested under the conditions of 300μs