Semiconductor device and method of manufacturing the same

A method of manufacturing a semiconductor device, comprising the steps of:

• forming a first diffusion layer of one conductivity type in a semiconductor layer, and forming a gate oxide film and a gate electrode on the semiconductor layer, and then forming a diffusion layer of an opposite conductivity type constituting a back gate region in the first diffusion layer of the one conductivity type by self-alignment using the gate electrode;
• and
• forming a second diffusion layer of the one conductivity type constituting a source region in the diffusion layer of the opposite conductivity type in a manner that the second diffusion layer of the one conductivity type overlapping the diffusion layer of the opposite conductivity type, and forming a third diffusion layer of the one conductivity type constituting a drain region in the first diffusion layer of the one conductivity type;
• wherein,
• in the step of forming the diffusion layer of the opposite conductivity type, an impurity concentration peak of the diffusion layer of the opposite conductivity type is formed in a portion of the first diffusion layer of the one conductivity type deeper than a junction region between the diffusion layer of the opposite conductivity type and the second diffusion layer of the one conductivity type.