In this work, a facile one-step KOH activation strategy has been developed toward synthesis of N/S-codoped hierarchical porous carbon spheres (NSHPCSs) from resorcinol-thiourea-formaldehyde sphere precursors. Quite different from the samples prepared by a traditional two-step activation that includes a successive KOH activation after carbonization, NSHPCSs possess a typical interconnected hierarchical porous structure comprised of macro-, meso-, and micropores with large pore volume and suitable pore size distribution, together with heteroatom doping of N and S. Originating from the above synergetic effect, the resultant NSHPCSs deliver a high specific capacitance of 295 F/g at 0.5 A/g, outstanding rate capability (78.6% retention at 20 A/g), and excellent cycling stability (95.2% retention over 5000 cycles). Furthermore, a symmetric supercapacitor achieves a high energy density of 7.36 Wh/kg at a power density of 100 W/kg. Thus, our study demonstrates an effective and simple approach of producing high-performance supercapacitor electrode materials for energy storage.