Abstract: This paper gives a novel multi-layer power-combining method which has the advantages of high density and lower insertion loss. This method can theoretically double the number of power-combining paths in the same size, that is, power increases by 3 dB. Therefore it is very suitable to be used in platforms with strict restrictions on the size and weight of power amplifiers. A 2 × 4-channel power amplifier with four layers of power-combining circuits is designed in 8 mm band based on the theoretical analysis and simulation optimization. The passive measurement result shows that the power-combining efficiency is higher than 91% over the range of 30-37 GHz. The amplifier is composed of eight GaN MMICs with typical output power of 16 W. In the condition of 35 μs pulse width and 10% duty cycle, a minimum output power of 123 W is observed, with a corresponding power gain of more than 14.9 dB and PAE better than 21.7%.