This brief presents the design methodology of an integrated KY dc-dc step-up converter with constant on-time (COT) control under discontinuous conduction mode (DCM) operation. The method improves the efficiency during the deep-light-load situation, and we analyze the design criteria of the flying capacitor as well as the COT controller of the KY converter under DCM. The simulation results verify that the design obtains higher conversion efficiency than the pulse width modulation controlled KY converter. The KY converter with COT control has been fabricated in 65-nm CMOS with a core area of 0.55 × 0.55 mm. The circuit uses an off-chip inductor of 12 nH and an output capacitor of 4 nF. The converter operates with a current load ranging from 500 μA to 10 mA with an output voltage ripple lower than 70 mV in the deep-light-load range.