An LDMOS device and method of fabrication are provided. The LDMOS device has a substrate with a source region and a drain region formed in the substrate. An insulating layer is provided on a portion of the substrate between the source and the drain region, such that a planar interface is provided between the insulating layer and a surface of the substrate. An insulating member is then formed on a portion of the insulating layer, and a gate layer is formed over part of the insulating member and the insulating layer. By employing such a structure, it has been found that a flat current path exists which enables the on-resistance to be decreased whilst maintaining a high breakdown voltage.