Semiconductor storage device and method of manufacturing the same

A semiconductor storage device comprising:

• a semiconductor substrate;
• a semiconductor layer formed on the semiconductor substrate;
• a first device isolation/insulation film formed in a trench, the trench formed in the semiconductor layer such that the trench has a longitudinal direction parallel with a first direction;
• a device formation region formed by separating the semiconductor layer by the first device isolation/insulation film such that the device formation region has a longitudinal direction parallel with the first direction;
• and
• a memory transistor disposed on the device formation region,
• the first device isolation/insulation film and the device formation region having an impurity of a first conductivity type, and
• an impurity concentration of the impurity of the first conductivity type in the first device isolation/insulation film being higher than that in the device formation region.