The advent of Ultra High Voltage (UHV) technologies for integrated circuit fabrication opens up new possibilities for the design of circuits that connect directly to the power distribution network, with applications in the design of compact power sources, domotics, smart-grids, etc. This project proposes the design, fabrication and characterization of circuits in an UHV technology, of which a fully integrated two terminal phase-cut dimmer was chosen as an example. At the time of writing this thesis, no commercially available integrated circuit exists that fully implements a phase cut dimmer, and no academic papers could be found referencing similar circuits. The circuit was designed on a 1µm UHV MOS technology in a silicon-on-insulator (SOI) wafer (XDM10 from XFAB). The dimmer can operate with a duty cycle of up to 95% power (80% time) and a load of up to 100W which is adequate for modern domestic dimmable LED lights. The total occupied silicon area is 6.5mm2 without pads. Because of technological limitations, the ﬁnal version of the dimmer is almost fully integrated. Two low voltage capacitors and four UHV diodes are outside the ASIC.