A magnetic or electromagnetic circuit component includes an embedded magnetic material (e.g., ferromagnetic) in an HDI structure with alternating dielectric and metal or winding layers. In one embodiment, the ferromagnetic material is situated in a substrate well, or cavity, with or without an adhesive. Alternatively, the ferromagnetic material is co-fired with the ceramic substrate and then machined to achieve a required core shape. An electroplating process is employed to construct the metal layers, such process including differential plating for varying the thickness of metal layers and/or other portions of the circuit. Laser ablation or any other suitable technique is employed to make through-holes for insertion of the posts of a ferromagnetic core plate used to complete a magnetic circuit, if required. Advantageously, a magnetic or electromagnetic component may have a height of less than about 0.1 inch. Furthermore, such magnetic or electromagnetic circuit components allow for very low inductance interconnections between these components and other circuit elements. Moreover, in a power supply, for example, not only can the complete power supply be built using HDI technology, but power density is increased at relatively low cost and at a high level of reproducibility.