All-solid-state planar on-chip micro-supercapacitors (MSCs) with superior energy and power characteristics were assembled via modified liquid-air interface self-assembly assisted by two-step reduction and photolithography. Planar on-chip electrodes based on reduced graphene oxide were provided with a nanoscale thickness of 3 nm and an interdigital electrode width of 8 μm. The planar on-chip MCSs showed a power density of 12.17 W cm−3 and an energy density of 40.97 mWh cm−3. Moreover, there were an extremely short time constant of 2.16 μs, and a superior capacitance retention of 97.3% after 10,000 cycles at 5000 V s−1.