A hierarchical porous polymeric network (HPPN) with ultrahigh specific surface area up to 2870 m² g⁻¹ was synthesized via a one-step ionothermal synthesis method without using templates. As the electrode material of supercapacitors, HPPN-400-30 exhibits a specific capacitance of 129 F g⁻¹ at 10 A g⁻¹ and demonstrates an excellent cycling stability with 99.93% capacitance retention after 10 000 cycles at 10 A g⁻¹. Furthermore, an all-solid-state supercapacitor (ASSS) based on HPPN-400-30 exhibits an energy density of 8.1 W h kg⁻¹ at the high power density of 5027 W kg⁻¹.