[en] Highlights: • Heterostructure with thin N-polar GaN/InN/GaN/In_0.9Al_0.1N layers. • 2D Sentarus TCAD hydrodynamic device model calibrated with experimental data. • DC and analog/RF performance is done by varying channel thickness (T_CH). • High I_ds =1.17 A/mm, peak g_m=2.9 S/mm, V_T ~ 0.728 V and I_ON/I_OFF of 3.23×10³ at V_ds =0.5 V. • f_t/f_max of 90/109 and 180/260 GHz for T_CH =2 nm at V_ds =0.5 V and 1 V are obtained. In this paper, we examined normally-OFF N-polar InN-channel Metal insulated semiconductor high-electron mobility transistors (MISHEMTs) device with a relaxed In_0.9Al_0.1N buffer layer. In addition, the enhancement-mode operation of the N-polar structure was investigated. The effect of scaling in N-polar MISHEMT, such as the dielectric and the channel thickness, alter the electrical behavior of the device. We have achieved a maximum drain current of 1.17 A/mm, threshold voltage (V_T) =0.728 V, transconductance (g_m) of 2.9 S mm⁻¹, high I_ON/I_OFF current ratio of 3.23×10³, lowest ON-state resistance (R_ON) of 0.41 Ω mm and an intrinsic delay time (τ) of 1.456 Fs along with high-frequency performance with f_t/ f_max of 90 GHz/109 GHz and 180 GHz/260 GHz for T_CH =0.5 nm at V_ds =0.5 V and 1.0 V. The numerically simulated results of highly confined GaN/InN/GaN/In_0.9Al_0.1N heterostructure MISHEMT exhibits outstanding potential as one of the possibility to replace presently used N-polar MISHEMTs for delivering high power density and frequency at RF/power amplifier applications.