The applicability of package-embedded spiral inductors to switching buck converters is demonstrated. In the first step, the design and characterization process of package-embedded spiral inductors is investigated via comprehensive full wave electromagnetic simulations, while considering a realistic, multi-layer flip-chip package. An interleaved multi-phase buck converter with an array of package-embedded spiral inductors is developed in the second step. The converter produces an output voltage of 0.9 V from 1.2 V input voltage while supplying a load current of 1 A. The flexibility of the package is exploited to obtain a relatively high inductance, enabling a reduced switching frequency. Lower switching frequency minimizes the dynamic loss, thereby increasing the power efficiency. According to the extracted results of the overall layout, power efficiency of approximately 89% is achieved with 3% output ripple voltage.