Semiconductor device and manufacturing method thereof

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

• forming an isolation region in a substrate to isolate an element formation region from the other region;
• forming depressions in respective upper surfaces of first and second regions of the isolation region opposing each other with the element formation region interposed therebetween;
• forming a gate electrode over the element formation region such that the gate electrode also extends over each of the first and second regions;
• and
• forming a pair of diffusion regions in the element formation region such that the pair of diffusion regions are spaced apart from each other in a channel length direction with reference to the gate electrode,
• wherein, in the step of forming the depressions, each of the depressions is formed to be depressed to a depth of not less than 5% of a channel width, and located under an upper surface of the element formation region, and
• wherein, in the step of forming the gate electrode, the gate electrode is formed such that a portion thereof is also present in each of the depressions.