a semiconductor device improving the characteristics of an integrated circuit in which transistors of different operation modes including a dynamic vth mos are mixed , comprising a plurality of mosfets each including a semiconductor active layer formed in an insulating layer on a substrate , a back side gate electrode facing its substrate side surface via a back side gate insulating film , and a front side gate electrode facing the opposite side surface from the semiconductor active layer via a front side gate insulating film , the plurality of mosfets including a first mosfet in which the back side gate electrode and the front side gate electrode are insulated and separated from each other and a second mosfet in which the back side gate electrode and the front side gate electrode are electrically connected , the back side gate insulating film of the dv - mos being thinner than the back side gate insulating film of the con - mos .