To minimize the electrical stress for electron-ejection of each flash memory cell, the variable word-line voltage (WP) method and the variable pulse width WP (WWP) method are proposed. Both methods make it possible to achieve high reliability while maintaining the total operating time of the conventional method, and both provide a sufficient disturb margin. Simulation results show that both methods reduce the maximum Fowler-Nordheim tunnel current density by 1.4 orders of magnitude compared to that of the conventional method, and the WWP method increases the number of verifications by much less than the WP method. This is expected to triple the charge-to-breakdown (Qbd) by decreasing the trap generation. A Qbd higher than the injection charge is obtained, as needed for high density flash memories.