Air-stable and area-selective doping strategies have eluded 2D materials and thus been a major bottleneck in realizing the plethora of semiconductor devices which require an built in electric field accessible from a p/n junction. Here, we demonstrate the possibility of p-doping through Vacancy Engineering, which unlike previous reports of molecular/substitutional doping is both area/dopant controllable and air-stable. Through Ar+ ions of appropriate energy and fluence bombarded on exfoliated MoS2, we demonstrate creation of sulfur vacancies that vary the S:Mo stoichiometry from 1.94 to 0.97 and hence controllably introduce p-type doping as verified using in-situ XPS and ex-situ Raman/PL measurements. FETs fabricated on Ar+ bombarded flakes show complete flip in polarity of carrier type from n-type to p-type when compared to Reference samples with the same metal contacts. Furthermore, selective Ar+ Bombardment only on contacts region shows effective hole injection with Ion/Ioff>103. Finally p/n junctions with Ar+ bombardment performed on one half of the flake demonstrate high rectification ratio (>104), forward currents (∼0.6 mA/cm2) and excellent photoresponse (Ilight/Idark ∼103) and responsivity (100-400 μA/W). © 2017 IEEE.