A
semiconductor device includes a substrate, a
semiconductor layer of a first
conductivity type having a single-
crystal structure, and a plurality of transistors each including a first gate
electrode provided above the
semiconductor layer with a first gate insulation film laid therebetween, a pair of
impurity regions of a second
conductivity type being provided in the semiconductor layer and each becoming a source or drain region, and a channel body of the first
conductivity type provided in the semiconductor layer at a portion between these
impurity regions. The device also includes a first gate line for common connection of the first gate electrodes of the transistors, a
dielectric layer provided above the substrate in an extension direction of the first gate line, for supporting the semiconductor layer under the pair of
impurity regions to thereby dielectrically isolate between the substrate and the semiconductor layer, a second gate
electrode provided above the substrate in such a manner as to underlie the channel bodies of the transistors and oppose the channel bodies with a second gate insulation film laid therebetween, the second gate
electrode having a
gate length larger than a onefold value of a
gate length of the first gate electrode and yet less than or equal to thrice the
gate length, and a second gate line provided above the substrate along the extension direction of the first gate line while being placed between portions of the
dielectric layer underlying the pair of impurity regions, the second gate line being for common connection of the second gate electrode.