This paper describes a smart-power-process which integrates a vertical 1200 V DMOS power transistor and low voltage CMOS circuits. For isolation purpose between the CMOS part and the high voltage power device, the local SIMOX process is used with a p-n junction in series. For the first time a scalable vertical 1200 V high power switching device has been combined with VLSI compatible CMOS to realize a resonant power supply circuit for compact fluorescent lamps. The functionality of the introduced process has been demonstrated by a monolithic integrated five terminal device for compact fluorescent lamps.