A highly efficient and broadband 10W GaN HEMT power amplifier (PA) is presented, which employs the hybrid PA mode, transferring between continuous Class-F and continuous inverse Class-F. A GaN PAis designed and realized based on this mode-transferring operation using the multisection matching transformers. Specifically, the multisection matching transformers consisting of stepped transmission-line sections with different characteristic impedances are preferred for its impedance matching. In this letter, the stepped transmission-line transformer is employed to optimize fundamental impedance and control the harmonic impedance directly. The proposed design strategy is experimentally verified by a 0.6-2.5 GHz PA design with 73.4% maximum power-added efficiency and 10 W output power. The footprint of the fabricated PAis ${55}\ \text{mm}\times {35}\ \text{mm}$ .