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This paper proposes a DC-DC buck power converter chip with a novel integrated PWM/PFM hybrid-mode control. The DC-DC converter chip with synchronous rectifier not only uses current-mode feedback control but also possesses constant-frequency-mode control and hybrid-mode control functions at the same time. Furthermore, the operational modes of the converter can be selected by an external voltage signal. In the part of constant-frequency-mode control, as the inductor current is below zero, the synchronous rectifier switch of the converter will be automatically turned off in order to reduce the loss of the reverse inductor current. About the hybrid-mode control, the operational modes of the converter can be judged by the proposed PWM/PFM hybrid-mode control circuit. When the converter is operated in CCM, the constant-frequency-mode control is applied and when the inductor current is in DCM, the converter is operated under the variable-frequency-mode control. At this moment, the switching frequency of the converter is designed to decrease proportionally with the load to reduce the high switching loss at light load. The synchronous rectifier switch will also be turned off in order to reduce the reverse conduction loss. All the above functions are integrated in one chip. Simulation and experimental results verify that the converter chip works functionally. The power converter chip with PWM/PFM hybrid-mode control proposed here is very suitable for the portable electronic products with the requirements of low voltage, low power, high efficiency, and wide load range.