Verification of an excessively high threshold voltage in a memory device

A memory system comprising:

• a memory device comprising a plurality of memory blocks;
• and
• a controller configured to perform bad block management on the plurality of memory blocks,
• wherein the bad block management comprises counting a number of excessive memory cells having a higher threshold voltage than a reference threshold voltage, among plural memory cells coupled to at least one word line, and generating a pass or fail signal based on whether the number of excessive memory cells is greater than or equal to an excess threshold value.

A method for operating a memory system, comprising:

• performing plural program operations to a memory device including a plurality of memory cells, wherein each of the plural program operations comprises selecting a word line to which target data are to be programmed based on a write command and programming the target data to the selected word line;
• determining at least one word line among plural word lines where the plural program operations are performed;
• counting a number of excessive memory cells having a higher threshold voltage than a reference threshold voltage, among plural memory cells coupled to the at least one word line;
• and
• generating a pass or fail signal based on whether the number of excessive memory cells is greater than or equal to an excess threshold value.