<p>Atomically thin two-dimensional (2D) semiconductors are promising candidates for beyond-silicon electronic devices. However, an excessive contact resistance due to ineffective or non-existent doping techniques hinders their technological readiness. Here, we unveil the doping mechanism of pure nitric oxide and demonstrate its effectiveness on wafer-scale grown monolayer and bilayer tungsten diselenide (1L- and 2L-WSe₂) transistors, where doping bands induced by nitric oxide can realign the Schottky barrier and approach p-type unipolar transport. This doping approach, combined with a scaled high-κ dielectric, yields WSe₂ transistors with high performance metrics. For monolayer WSe₂, we achieved an on-state current of 300 μA/μm (at a drain-to-source voltage of –1 V and overdrive voltage of –0.8 V), contact resistance of 875 Ω·μm, peak transconductance of 400 μS/μm, and a subthreshold swing of 70 mV/dec, while preserving on/off ratios &gt;10⁹, minimal variability, and good stability over 24 days under moderate thermal conditions. For bilayer WSe₂, the devices exhibit an on-state current of 448 μA/μm and contact resistance of 390 Ω·μm, further showcasing the scalability and effectiveness of the NO doping method. Our findings establish NO doping as a promising technique for realizing high-performance p-type 2D transistors and advancing next-generation ultra-scaled electronic devices.</p>