Bias conditions for improving the efficiency of repairing, programming and erasing the threshold voltages of non-volatile memory devices. A positive voltage is applied to the source region of a non-volatile memory cell. The control gate of the memory cell is applied with another positive voltage higher the voltage at the source region. The difference between the two voltages is proportional to the desired final threshold voltage. The drain region can be applied with a positive voltage directly from the power supply of the memory device. A negative voltage is applied to the bulk of the memory device so that a large electric field across the control gate and the bulk can induce hot-electron injection. By selecting the proper voltage level at the control gate, the method can be used for the repair, program or erase operation of memory devices.