A semiconductor memory device comprises a substrate; a semiconductor layer of a first conductive type isolated from the substrate by an insulator layer; a memory transistor having a gate electrode, a drain and a source regions of a second conductive type formed in the semiconductor layer, and a channel body of the first conductive type formed in the semiconductor layer between the regions, the memory transistor operative to store data as a state of majority carriers accumulated in the channel body; an impurity-diffused region of the first conductive type formed at a location in contact with the upper surface of the drain region, the impurity-diffused region having a higher impurity concentration of the first conductive type than an impurity concentration of the second conductive type in the drain region; and a write transistor including a bipolar transistor having the impurity-diffused region as an emitter region, the drain region as a base region and the channel body as a collector region, the write transistor operative to write data in the memory transistor.