A semiconductor base material stands on a substrate in a vertical direction or extends in a horizontal direction. Between first and second impurity layers disposed at the ends of the semiconductor base material, first and second gate insulating layers and first and second gate conductor layers are disposed around the semiconductor base material. A memory write operation is performed where voltages are applied to the first and second impurity layers and the first and second gate conductor layers to cause an impact ionization phenomenon to occur in a channel region, and among generated groups of electrons and positive holes, the group of electrons are discharged from the channel region and some of the group of positive holes are retained in the channel region. A memory erase operation is performed where the retained group of positive holes are discharged via any of or both of the first and second impurity layers.