We determine the thermodynamic properties of a class of spherically symmetric and static black holes in AdS4 with magnetic charges and scalar hair. These black holes are solutions in 4d N=2 gauged supergravity that arise from eleven-dimensional supergravity compactified on S^7. At zero temperature, they preserve supersymmetry and hence are stable. At non-zero temperatures, we explore in detail the canonical ensemble and stability of solutions and find a first order phase transition between small and large hairy black holes. We discuss some consequences for the AdS/CFT correspondence, where the transition emerges as a liquid-gas phase transition in the dual three-dimensional field theory on R x S^2 with magnetic flux through S^2.