Rigid three-dimensional (3D) Ni₃S₄ nanosheet frames assembled from ultrathin nanosheets are synthesized via a facile solvothermal method. Compared to flat Ni₃S₄ sheets, 3D Ni₃S₄ nanosheet frames have both a high free volume and high compressive strength. They can deliver a very high specific capacitance of 1213 F g⁻¹ with good rate performance. In addition, these 3D Ni₃S₄ nanosheet frames are stabilized by plastically deformed ridges. The stabilized nanosheet frames did not unfold or collapse during electrochemical tests, and thus showed enhanced cycling ability.