This paper presents numerical simulation and characterization of high-power Gallium Nitride Junctionless Accumulation Mode Nanowire FET (GaN-JAM-NWFET) which has improved analog performance and is suitable for high-frequency applications. In GaN-JAM-NWFET, GaN and Aluminium Oxide (Al2O3) replace Silicon (Si) and Silicon Oxide (SiO2), respectively. Because of the larger bandgap and strong breakdown field, GaN based devices can handle higher voltages and powers with good carrier transport qualities, which permit a higher driving current than Si devices. Moreover, GaN-JAM-NWFET has a better performance than GaN based Junctionless (JL) NWFET due to the benefit of JAM structure over JL device, having increased carrier mobility in the lightly doped channel. These cumulative benefits of GaN with JAM manifest improvement in drain current, output conductance, subthreshold swing, transconductance, gate capacitance, cut-off frequency, Frequency Transconductance Product (FTP), Gain Frequency Product (GFP), Gain Transconductance Frequency Product (GTFP), intrinsic gain, Unilateral Power Gain (UPG) and Maximum Transducer Power Gain (MTPG) in proposed GaN-JAM-NWFET among GaN-JL-NWFET, Si based JAM NWFET, and Si-JL NWFET devices. The S-parameters such as transmission coefficients (S12 & S21) and reflection coefficients (S11 & S22) also confirm the proposed GaN-JAM-NWFET has better small signal performance than other devices.