High performance p-type field-effect transistors (p-FETs) based on single-layered WSe₂ with chemically doped source/drain contacts and high-κ gate dielectrics are reported. The top-gated monolayer transistors exhibit a high effective hole mobility of ~250 cm²/Vs, a perfect subthreshold swing of ~60 mV/dec, and an I_ON/I_OFF ratio of >10⁶ at room temperature. The key to achieving these results is the use of high work function Pd contacts and degenerate surface doping of the contacts via patterned NO₂ chemisorption on WSe₂. This approach significantly reduces contact resistance and enables the demonstration of p-FETs with excellent performance. WSe₂ is a layered semiconductor with a bulk indirect bandgap of ~1.2 eV. Bulk WSe₂ FETs have shown an intrinsic hole mobility of up to 500 cm²/Vs, but they suffer from poor I_ON/I_OFF ratios and ambipolar behavior. Here, single-layered WSe₂ was obtained via mechanical exfoliation and characterized using optical and AFM microscopy. The thickness of the single layer was determined to be ~0.7 nm, consistent with literature data. The challenge of forming ohmic contacts to WSe₂ is addressed by exploring different metal contacts, including Pd, Ag, Ni, Au, Ti, and Gd. Pd was found to form the lowest resistance contact to the valence band of WSe₂ for hole transport, resulting in the highest unit-width normalized ON currents. The use of NO₂ molecules as a p-type surface dopant was explored, leading to significant improvements in carrier mobility and reduced contact resistance. The surface doping of WSe₂ with NO₂ resulted in a heavily doped channel with a 2D carrier density of ~2.2×10¹² cm⁻² and a doping concentration of ~3.1×10¹⁹ cm⁻³. This level of doping is sufficient to make the material degenerately doped, with the Fermi level lying ~16 meV below the valence band edge. The NO₂ doping is reversible, as the molecules desorb from the WSe₂ surface upon exposure to ambient air. Patterned p-doping of WSe₂ was used to fabricate top-gated ML-FETs with self-aligned, chemically doped S/D contacts. The devices exhibited a significant improvement in ON current, with a ~1000x enhancement after surface doping. The I_ON/I_OFF ratio reached >10⁶, demonstrating the excellent performance of the p-FETs. The transfer characteristics at room temperature showed a perfect subthreshold swing of ~60 mV/dec, approaching the theoretical limit for a MOSFET. The effective hole mobility of the top-gated WSe₂High performance p-type field-effect transistors (p-FETs) based on single-layered WSe₂ with chemically doped source/drain contacts and high-κ gate dielectrics are reported. The top-gated monolayer transistors exhibit a high effective hole mobility of ~250 cm²/Vs, a perfect subthreshold swing of ~60 mV/dec, and an I_ON/I_OFF ratio of >10⁶ at room temperature. The key to achieving these results is the use of high work function Pd contacts and degenerate surface doping of the contacts via patterned NO₂ chemisorption on WSe₂. This approach significantly reduces contact resistance and enables the demonstration of p-FETs with excellent performance. WSe₂ is a layered semiconductor with a bulk indirect bandgap of ~1.2 eV. Bulk WSe₂ FETs have shown an intrinsic hole mobility of up to 500 cm²/Vs, but they suffer from poor I_ON/I_OFF ratios and ambipolar behavior. Here, single-layered WSe₂ was obtained via mechanical exfoliation and characterized using optical and AFM microscopy. The thickness of the single layer was determined to be ~0.7 nm, consistent with literature data. The challenge of forming ohmic contacts to WSe₂ is addressed by exploring different metal contacts, including Pd, Ag, Ni, Au, Ti, and Gd. Pd was found to form the lowest resistance contact to the valence band of WSe₂ for hole transport, resulting in the highest unit-width normalized ON currents. The use of NO₂ molecules as a p-type surface dopant was explored, leading to significant improvements in carrier mobility and reduced contact resistance. The surface doping of WSe₂ with NO₂ resulted in a heavily doped channel with a 2D carrier density of ~2.2×10¹² cm⁻² and a doping concentration of ~3.1×10¹⁹ cm⁻³. This level of doping is sufficient to make the material degenerately doped, with the Fermi level lying ~16 meV below the valence band edge. The NO₂ doping is reversible, as the molecules desorb from the WSe₂ surface upon exposure to ambient air. Patterned p-doping of WSe₂ was used to fabricate top-gated ML-FETs with self-aligned, chemically doped S/D contacts. The devices exhibited a significant improvement in ON current, with a ~1000x enhancement after surface doping. The I_ON/I_OFF ratio reached >10⁶, demonstrating the excellent performance of the p-FETs. The transfer characteristics at room temperature showed a perfect subthreshold swing of ~60 mV/dec, approaching the theoretical limit for a MOSFET. The effective hole mobility of the top-gated WSe₂