We report on doped AlGaN/GaN heterostructures with very high values of the sheet electron concentration (up to approximately 1.5×1013 cm−2), high Hall mobility (on the order of 800 cm2/Vs) and high sheet concentration‐mobility product (up to approximately 1016 1/Vs). Transmission line model measurements of the contact resistance to these layers show that series resistance is considerably reduced by doping the GaN channel. A contact resistance of 2.3 Ω mm is demonstrated for the structure with the highest sheet carrier concentration, which corresponds to ≊8.8×10−5 Ω cm2 specific contact resistance.