Abstract: A method for fabrication of a high-voltage, high-frequency MOS-transistor combines a deep n-well and a p-well process and the formation of an extended drain region (45), and a channel region (31), the channel having a short length and becoming well aligned with the gate edge. The deep n-well (11) and the p-well (19) are both produced by ion implantation. The method is compatible with a standard CMOS process and gives low manufacturing costs, increased breakdown voltage, better overall high-frequency performance, and the prevention of the “body effect” occurring by isolation of the p-well.