Semiconductor device and method of manufacturing the same

A method of manufacturing a semiconductor device, comprising:

• forming at least an insulating film on a semiconductor substrate;
• etching the insulating film and the semiconductor substrate by a photolithography process, thereby forming a first element isolation trench with a first opening width and a second element isolation trench with a second opening width larger than the first opening width, the first and second element isolation trenches having respective inner surfaces, the second element isolation trench having an inner surface and bottom;
• forming a first element-isolating insulation film on the inner surfaces of the first and second element isolation trenches;
• forming a second element-isolating insulation film on the first element-isolating insulation film formed in first and second element isolation trenches so that the second element-isolating insulation film has such a film thickness as to be capable of filling the first element isolation trench;
• removing the second element-isolating insulation film formed in the second element isolation trench;
• and
• filling the second element isolation trench with a third element-isolating insulation film so that the third element-isolating insulation film is located over the first element-isolating insulation film formed in the second element isolation trench which is exposed as a result of removal of the second element isolation trench.