A new harmonic termination that controls the waveform of the drain current to be rectangular is developed for high-efficiency power amplifier modules. Its harmonic termination is a short circuit at the third harmonic and a non-short circuit at the second harmonic. It is found experimentally and confirmed by simulation that the load-matching condition at the third-order harmonic improves the efficiency of a transistor by more than 13%. By using this tuning, 57.7% power-added efficiency of the module is achieved at the output power of 29.9 dBm with ACP of -50 dBc, NACP of -65 dBc at 925 MHz and Vdd of 3.5 V.