Semiconductor memory device equipped with memory transistor and peripheral transistor and method of manufacturing the same

A semiconductor memory device provided with a memory cell region, having first gate electrodes and a selecting transistor region having second gate electrodes, comprising:

• the first gate electrodes arranged a first distance apart from each other on a semiconductor substrate;
• the second gate electrodes arranged a second distance, which is larger than the first distance, apart from each other on the semiconductor substrate;
• first diffusion layers formed in the semiconductor substrate, the first diffusion layers sandwiching the first gate electrodes;
• second diffusion layers formed in the semiconductor substrate, the second diffusion layers sandwiching the second gate electrodes;
• a first insulating film formed on the first diffusion layers and covering the first diffusion layers;
• second insulating films formed on the side surfaces of the second gate electrodes;
• third insulating films formed on the second diffusion layers and covering the second diffusion layers;
• first silicide films formed on the first gate electrodes;
• and
• second silicide films formed on the first gate electrodes;
• wherein the respective thicknesses A1 and A2 of the first and second insulating films as formed satisfy the relationships X/2≦A1≦Y/2 and X/2≦A2≦Y/2, where X represents the first distance, and Y represents the second distance.