In a semiconductor memory device, a capacitor with a trench having a laterally expanded bottom part is provided, the area above the laterally expanded part being provided for a transistor and cell separation, this resulting in an increase in the degree of integration. This laterally expanded part is formed by etching a silicon oxide film which is sandwiched between a substrate and a silicon layer, and is obtained by forming a depression in a semiconductor substrate beforehand. A silicon layer or another semiconductor substrate is laminated by bonding to a semiconductor substrate such as this into which is formed a depression, a trench which extends to this depression being formed, and the required films being formed to obtain the desired trench capacitor. By forming an oxide film on all of or the depression part of the semiconductor substrate into which is formed the depression, it is possible to eliminate the influence of radiation, by improving insulation properties.