A memory device includes a semiconductor column extending above a substrate, a first conductive layer on a first side of the semiconductor column, a second conductive layer on a second side of the semiconductor column, opposite to the first conductive layer, a third conductive layer above or below the first conductive layer and on the first side of the semiconductor column, a fourth conductive layer on the second side of the semiconductor column, opposite to the third conductive layer, and a bit line connected to the semiconductor column. During reading in which a positive voltage is applied to the bit line, first, second, third, and fourth voltages applied to the first, second, third, and fourth conductive layers, respectively, wherein the first voltage and the third voltage are higher than each of the second voltage and the fourth voltage, and the third voltage is higher than the first voltage.