Abstract: A dual-gate insulated gate field effect device (1) such as a MOS tetrode has an active device area (3) in which adjacent source regions (5) are separated by and spaced apart from an intervening drain region (6) to define a respective conduction channel region (7) between each source and drain region (5 and 6). An insulated gate structure (10) has first insulated gate sections (11) forming an inner insulated gate (110) connected so as to surround each drain region 6 and second insulated gate sections (12) provided between the first insulated gate sections (11) and the source regions (5) and forming an outer insulated gate (120). Ends (11a,12a) of the insulated gate sections (11 and 12) extend onto the surrounding field oxide (4) to connect with respective first and gate conductors (13 and 14).