The materials used for high-frequency power transformers are under permanent improvement. Soft magnetic ferrites designed for high operating frequencies and equipped with increasing depolarisation current (DC)-bias behavior are state of the art for a lot of applications. Along with the limited DC resistance, the dielectric properties of the grain boundaries have an additional influence on the frequency-dependent drop of the AC resistance. Power applications of high-frequency products comprise transformers in switch-mode power supplies, power chokes, and electronic lamp ballast devices. There are two important trends for the development: the miniaturization of power transformers and the demand for increasing transmitted power. The inductivity at working temperature is important for the application of the transformer. The application of power transformer ferrites at different frequencies results in shifted positions of the power loss minimum. The manufacturing of ferrite cores requires considerable technological measures in order to transfer typical material properties to extraordinary component geometries.