A NAND memory array has a first dielectric layer formed on a first portion of a semiconductor substrate and a second dielectric layer formed on a second portion of the semiconductor substrate and adjoining the first dielectric layer. The first dielectric layer is thicker than the second dielectric layer. A first gate stack is formed on the first dielectric layer to form a drain select gate. A string of second gate stacks is formed on the second dielectric layer to form a NAND string of floating-gate memory cells. A first end of the NAND string is coupled in series with the drain select gate. A third gate stack is formed on the second dielectric layer to form a source select gate. A second end of the NAND string is coupled in series with the source select gate.