Memories and their formation are disclosed. One such memory has a first array of first memory cells extending in a first direction from a first surface of a semiconductor. A second array of second memory cells extends in a second direction, opposite to the first direction, from a second surface of the semiconductor. Both arrays may be non-volatile memory arrays. For example, one of the memory arrays may be a NAND flash memory array, while the other may be a one-time-programmable memory array.