The small-signal model of conventional and proposed GaN HEMT with updated parameter of C \(\mathrm {_{DS2}}\) at a gate length (L \(\mathrm {_G}\) ) of 0.5 \(\mu \) m is proposed and analyzed. Intrinsic and extrinsic parameter values are extracted for the bias condition, V \(\mathrm {_{DS}}\) = 3 V, and 5 V at V \(\mathrm {_{GS}}\) = 1 V. The large-signal model analysis including output characteristics, Power Added Efficiency (PAE), gain and Monte Carlo for average power and output noise is performed by considering the approximate small-signal model. The drain current of the proposed GaN HEMT is observed to be 177 mA/mm which is 16% higher than conventional GaN HEMT. For the proposed GaN HEMT, the PAE shows a slight increment of 0.8%, 0.5%, and 0.1% at 61 GHz, 64 GHz, and 67 GHz in comparison to conventional GaN HEMT. Similarly, gain increases by 1%, 0.9%, 1.4% for proposed GaN HEMT under the exact same condition. The stability of the proposed GaN HEMT as measured by using Monte Carlo analysis is 5% which is within the 10% limit for any standard circuit.