This paper presents the design and electrical performance of transformers with magnetic thin films for on-chip power conversion and isolation. The inductance of the devices is greatly enhanced by the use of a high-permeability magnetic material as a solenoid core, resulting in an inductance density of 108 nH/mm². The total thickness of the transformer structures is <30 μm with a volume inductance density of 3.6 μH/mm³. By laminating the magnetic core, losses are well controlled leading to a peak quality factor (Q) of 16 at 40 MHz.