Programming nonvolatile memory device using program voltage with variable offset

A method of programming a nonvolatile memory device, the method comprising:

• applying at least one test program pulse to selected memory cells located in a scan read area of the nonvolatile memory device;
• performing a scan read operation on the selected memory cells, following the application of the at least one test program pulse, to determine a read operation voltage at which a predetermined number of one-shot upper cells are identified;
• calculating an offset voltage based on the difference between the determined read operation voltage and a reference voltage;
• setting a program start bias using the offset voltage;
• and
• executing at least one program loop using the program start bias,
• wherein the scan read operation comprises, increasing/decreasing the read operation voltage, performing another read operation, by applying the increased/decreased read operation voltage, iterating operations the increasing/decreasing and the performing another read operation until the number of off cells detected during the other read operation exceeds a predetermined number, and establishing the read operation voltage applied in the last iterations the increasing/decreasing and the performing another read operation as an offset index.