Method of operating semiconductor memory device and memory system including semiconductor memory device

A method of operating a semiconductor memory device including a plurality of pages, and flag cells corresponding to the plurality of pages, respectively, the method comprising:

• receiving a program command, an address, and data;
• when the address corresponds to a Least Significant Bit (LSB) page of a selected page, reading page data from the LSB page of the selected page;
• reading flag data from a flag cell corresponding to the selected page;
• determining whether the number of bits of data corresponding to a program state among the page data is greater than a threshold value when the flag data does not correspond to a predetermined value;
• and
• outputting a state fail signal without performing a program operation on the selected page based on a result of the determination.

A memory system comprising:

• a semiconductor memory device including a plurality of memory blocks, each of which includes a plurality of pages;
• and
• a controller suitable for transmitting a special program command to the semiconductor memory device when a program operation is performed on a page within a first memory block, and transmitting a normal program command to the semiconductor memory device when a program operation is performed on a page within a second memory block,
• wherein the semiconductor memory device reads page data from a selected page in response to the special program command, determines whether the number of bits of data corresponding to a program state among the page data is greater than a threshold value, and outputs a state fail signal without programming the selected page based on a result of the determination.