We report the effects of Mg doping in the barriers of semipolar (202¯1) multiple-quantum-well light-emitting diodes (LEDs) with long emission wavelengths (>500 nm). With moderate Mg doping concentrations (3 × 1018–5 × 1018 cm−3) in the barriers, the output power was enhanced compared to those with undoped barriers, which suggests that hole transport in the active region is a limiting factor for device performance. Improved hole injection due to Mg doping in the barriers is demonstrated by dichromatic LED experiments and band diagram simulations. With Mg-doped AlGaN barriers, double-quantum-well LEDs with orange to red emission (λ > 600 nm) were also demonstrated.