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In this paper, DC, transient, and RF performances among AlGaN/GaN HEMTs with a no field plate structure (basic), a conventional gate field plate structure (GFP), and a double floating field plate structure (2FFP) were studied by utilizing SILVACO ATLAS 2D device technology computer-aided design (TCAD). The peak electric fields under the gate in drain-side can be alleviated effectively in 2FFP devices, compared with basic and GFP devices, which promotes the breakdown voltage (BV) and suppresses the current collapse phenomenon. As a result, the ON-resistance increase caused by the current collapse phenomena is dramatically suppressed in 2FFP ~19.9% compared with GFP ~49.8% when a 1 ms duration pre-stress was applied with Vds = 300 V in the OFF-state. Because of the discontinuous FP structure, more electric field peaks appear at the edge of the FFP stacks, which leads to a higher BV of ~454.4 V compared to the GFP ~394.3 V and the basic devices ~57.6 V. Moreover, the 2FFP structure performs lower a parasitic capacitance of Cgs = 1.03 pF and Cgd = 0.13 pF than those of the GFP structure (i.e., Cgs = 1.89 pF and Cgd = 0.18 pF). Lower parasitic capacitances lead to a much higher cut-off frequency (ft) of 46 GHz and a maximum oscillation frequency (fmax) of 130 GHz than those of the GFP structure (i.e., ft = 27 GHz and fmax = 93 GHz). These results illustrate the superiority of the 2FFP structure for RF GaN HEMT and open up enormous opportunities for integrated RF GaN devices.