Contact resistance limits the performance of organic field‐effect transistors, especially those based on high‐mobility semiconductors. Despite intensive research, the nature of this phenomenon is not well understood and mitigation strategies are largely limited to complex schemes often involving co‐evaporated doped interlayers. Here, this study shows that solution self‐assembly of a polyelectrolyte monolayer on a metal electrode can induce carrier doping at the contact of an organic semiconductor overlayer, which can be augmented by dopant ion‐exchange in the monolayer, to provide ohmic contacts for both p‐ and n‐type organic field‐effect transistors. The resultant 2D‐doped profile at the semiconductor interface is furthermore self‐aligned to the contact and stabilized against counterion migration. This study shows that Coulomb potential disordering by the polyelectrolyte shifts the semiconductor density‐of‐states into the gap to promote extrinsic doping and cascade carrier injection. Contact resistivities of the order of 0.1–1 Ω cm² or less have been attained. This will likely also provide a platform for ohmic injection into other advanced semiconductors, including 2D and other nanomaterials.