Measurements of acceptor activation energy in p – n junctions based on superlattices of AlN ~1.25 nm thick! and Al0.08Ga0.92(In!N ~0.5 nm thick!, with the average AlN content greater than 0.6, are reported. Structural characteristics of superlattices were determined using transmission electron microscopy and x-ray diffraction. p – n junctions in mesa-etched diodes exhibit low leakage current densities of 3310210 A/cm2 at near zero bias. Acceptor activation energy of 207610 meV, obtained from the temperature dependence of the forward current, is very similar to that of uniform alloy of Al0.08Ga0.92N that constitutes the well material. The acceptor activation energy thus appears controlled by the well material and remains low despite high average AlN content and large band gap.