PURPOSE: To effectively prevent a kink effect by forming a first gate region which has a first gate terminal and has a conductivity type opposite to that of a first one and forming a second region of a second conductivity type which is connected to the first gate terminal. CONSTITUTION: An n -source region 3 is formed on a back oxide 2, and then a source terminal 4 is formed on the n -source region 3 to supply source voltage Vs to. A first p -gate region 4, an n -intermediate region 5, and a second p -gate region 6 are also formed on the back oxide 2 and oxide films 7, 8 are formed on the first gate region 4 and the second gate region 6 respectively. Electrodes 9, 11 formed on the first and the second gate region 4, 6 respectively are connected to a common gate voltage VGS, and therefore (n) channels are formed in the first and the second gate regions. On the back oxide 2, a drain region 14 is formed and is provided with a terminal 15 to supply a drain voltage VDS to. A width/length ratio of the first gate region 4 is 50/2, and that of the second gate region 6 is 50/1.