Semiconductor device and method of manufacturing the same

A semiconductor device comprising:

• a semiconductor substrate;
• a transistor comprising a gate insulation film on the semiconductor substrate and a gate electrode on the gate insulation film;
• and
• a device isolating insulation film formed after formation of at least a portion of the gate electrode and comprising a first portion which extends from a surface of the semiconductor substrate to an inner part of the semiconductor substrate and a second portion which protrudes from the semiconductor substrate, wherein a side surface of the second portion is in direct contact with a side surface of the gate electrode at least partially and a cross section of the gate electrode increases from a bottom surface of the gate electrode facing the semiconductor substrate to a top surface of the gate electrode, and a cross section of the second portion decreases from a bottom surface of the second portion facing the substrate to a top surface of the second portion.