The present invention relates to a highly packaged semiconductor memory, and more particularly to a memory cell having a trench capacitor for use in a CMOS memory. The present invention discloses a semiconductor memory employing memory cells each constructed of a trench type charge storage capacitor formed within a substrate, and a switching transistor; one electrode of the capacitor having a sheath-shaped structure which is electrically continuous with the Si substrate at a bottom of a groove and whose sideward periphery is covered with an insulator, the other electrode of the capacitor having a part which is buried inside the sheath electrode and another part which is electrically connected with an impurity diffused layer to function as a source region of the transistor. Further, a structure in which a voltage of 1/2 V.sub.cc can be applied to a plate electrode of a memory cell having a trench capacitor is disclosed.