The fastest ever 4.2 Gbps 3D-Solid State Drive (SSD) with multi-level cell (MLC) NAND flash memories is proposed. The proposed NAND channel number detector automatically detects the number of channels, that is, the number of NAND chips written at the same time. Based on the number of channels, the intelligent program-voltage booster adaptively optimizes the switching clock. As a result, the proposed 3D-SSD realizes both the fastest write and the lowest energy consumption. In the random write with a small data size, the booster operates in an energy saving mode and decreases the energy consumption of the booster by 32%. In the sequential write with a large data size, up to 24 channels are activated. The booster operates in a high-speed mode to accelerate the pumping. The SSD write speed increases by 60%.