Microstructures, and especially grain boundary populations, are characterized in a γ/γ′ nickel-base superalloy submitted to various thermomechanical treatments involving hot deformation and subsequent supersolvus annealing. The resulting microstructures consist of equiaxed grains, including twins. Both the grain size and the amount of twin boundaries are dependent on the processing parameters, which demonstrates that grain boundary engineering is applicable to those materials. The mechanisms involved are discussed, taking into account the hot-working conditions. © 2010 Acta Materialia Inc.