A nonvolatile semiconductor memory device of the charge trap type is initialized by reading the memory cells in the device to determine which charge traps hold less than a predetermined minimum charge and injecting charge into these charge traps until all of the charge traps in the device hold at least the predetermined minimum charge. The charge traps are then programmed selectively with data. The initialization procedure shortens the programming procedure by narrowing the initial distribution of charge in the charge traps, and leads to more reliable reading of the programmed data.