In this paper, a new method for improvement of the efficiency of Doherty power amplifier (PA) at dual-frequencies is presented. The structure of the conventional Doherty PA using equal LDMOS devices for main Class-AB and peaking Class-C amplifiers is designed. Compensation line with phase shifter composed of PIN diode is adapted and demonstrated experimentally for removing reactance components of the output impedance at each frequency. Adequate output phase of the Doherty PA at each frequency is adjusted using switching operation of PIN diode. In order to evaluate the switching performance of the proposed method, measurements have been carried out at two sample frequencies (2.1 GHz and 2.2 GHz). According to the on (2.1 GHz) and off-state (2.2 GHz) of PIN diode, compensation line adjusts exact load impedance at each frequency. The proposed 100 W Doherty PA provides power added efficiency (PAE) over 47% at 6-dB back-off power region (44 dBm). At 2.1 GHz, Doherty PA at on-state shows about 5% enhancement of PAE comparison with Doherty PA at off-state.