DC-DC power converters with GaN switches, magnetic inductors and CMOS power drivers integrated through face-to-face wafer bonding techniques are provided. In one aspect, an integrated DC-DC power converter includes: a Si CMOS chip having at least one Si CMOS transistor formed thereon; a GaN switch chip, bonded to the Si CMOS chip in a face-to-face manner, having at least one GaN transistor formed thereon; and an on-chip magnetic inductor present either on the Si CMOS chip or on the GaN switch chip. A method of forming an integrated DC-DC power converter is also provided.