A 3D memory device includes an improved dual gate memory cell. The improved dual gate memory cell has a channel body with opposing first and second side surfaces, charge storage structures on the first and second side surfaces, and a gate structure overlying the charge storage structures on both the first and second side surfaces. The channel body has a depth between the first and second side surfaces less than a threshold channel body depth, combined with the gate structure which establishes an effective channel length of the cell greater than a threshold length. The combination of the channel body depth and effective channel length are related so that the cell channel body can be fully depleted, and sub-threshold leakage current can be suppressed when the memory cell has a high threshold state under a read bias.