We report a new strategy for fabricating 2D/2D low-resistance ohmic contacts for a variety of transition metal dichalcogenides (TMDs) using van der Waals assembly of substitutionally doped TMDs as drain/source contacts and TMDs with no intentional doping as channel materials. We demonstrate that few-layer WSe₂ field-effect transistors (FETs) with 2D/2D contacts exhibit low contact resistances of ∼0.3 kΩ μm, high on/off ratios up to >10⁹, and high drive currents exceeding 320 μA μm^–1. These favorable characteristics are combined with a two-terminal field-effect hole mobility μ_FE ≈ 2 × 10² cm² V^–1 s^–1 at room temperature, which increases to >2 × 10³ cm² V^–1 s^–1 at cryogenic temperatures. We observe a similar performance also in MoS₂ and MoSe₂ FETs with 2D/2D drain and source contacts. The 2D/2D low-resistance ohmic contacts presented here represent a new device paradigm that overcomes a significant bottleneck in the performance of TMDs and a wide variety of other 2D materials as the channel materials in postsilicon electronics.