NOVELTY - The device (100) has a source region (104), a drain region (106), and a drain extension region (108) which are formed in a substrate. An insulation layer (110) is adjacent to drain extension region. The gate layer (112) and field plate (114) are formed within and on the insulation layer. The field plate is located adjacent to drain extension region, and is insulated from gate layer and source region, such that a voltage is applied to field plate independent from voltages applied to gate layer and source region. The gate layer and the field plate are made of polysilicon.    USE - Semiconductor device such as transistor of N-type metal oxide semiconductor (NMOS), P-type metal oxide semiconductor (PMOS), and complementary metal oxide semiconductor (CMOS) types, e.g. silicon on insulator (SOI) based transistor, fin FET, and trench FET of circuit (all claimed) such as relay driver circuit, motor driver circuit, and lamp driver circuit used in power device for automobile and lighting applications, and computing device such as smartphone, tablet computer, and laptop computer.    ADVANTAGE - Since the doping level in the drain extension region can be made higher and the appropriate voltages are applied to the field plate in the on state and off state, the on state resistance of the semiconductor device can be lowered without degrading the breakdown voltage. Since the on-resistance of the semiconductor device is reduced, the footprint and size of the semiconductor device can be reduced. By putting the field plate adjacent to the drain extension region, the reduced surface field (RESURF) effect can be used to decrease the resistance associated with the drain extension region. By grounding the field plate during the off state of the semiconductor device, the drain extension region can be more easily depleted in the off state and the high voltages can be supported by the semiconductor device at higher drain extension doping. The overall space requirement for transistor circuit is reduced even though an extra space is needed for drive circuit.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a circuit comprising semiconductor device; and    (2) a method for operating semiconductor device.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of the semiconductor device.    Semiconductor device (100)    Source region (104)    Drain region (106)    Drain extension region (108)    Insulation layer (110)    Gate layer (112)    Field plate (114)