A
semiconductor memory device having a
memory cell region and a
peripheral circuit region, and a method of manufacturing such a
semiconductor memory device, are proposed, in which trench grooves are formed to be shallow in the
memory cell region in order to improve the yield, and trench grooves are formed to be deep in the
high voltage transistor region of the
peripheral circuit region, in particular in a
high voltage transistor region thereof, in order to improve the element isolation withstand
voltage. A plurality of
memory cell transistors having an ONO layer 15 serving as a charge accumulating insulating layer are provided in the memory
cell region, where element isolation grooves 6 for these memory
cell transistors are narrow and shallow. Two types of transistors, one for
high voltage and the other for
low voltage, having gate insulating
layers 16 or 17, which are different from the ONO layer 15 in the memory
cell region, are provided in the
peripheral circuit region, where at least element isolation grooves 23 for
high voltage transistors are wide and deep. In this way, it is possible to improve the degree of integration and yield in the memory
cell region, and secure withstand
voltage in the peripheral circuit region.