Memory device for performing read operation and method of operating the same

A memory device comprising:

• a plurality of memory cells connected to a word line;
• an operation controller configured to perform a program operation that stores multi-page data, each including a plurality of bits in the plurality of memory cells, and configured to perform a read operation that obtains the multi-page data that is stored in the plurality of memory cells, the program operation including a first program step and a second program step, the multi-page data including a plurality of logical pages;
• and
• a read voltage controller configured to control the operation controller to determine whether a program step Is performed up to the first program step or the second program step on the plurality of memory cells based on the number of 0s or 1s that are included in sensing data that is obtained by sensing data that is stored in the plurality of memory cells by using a second read voltage, in response to a read command that provides instruction to read a logical page among the plurality of logical pages, and configured to sense the data that is stored in the plurality of memory cells by using a first read voltage with a voltage that is lower than the second read voltage when a program step of the plurality of memory cells is the first program step.

A method of operating a memory device for reading data that is stored in memory cells by using a first read voltage or a second read voltage, the method comprising:

• reading the data that is stored in the memory cells by using the second read voltage;
• counting the number of off cells among the memory cells by using the second read voltage;
• and
• reading the data that is stored in the memory cells by using the first read voltage with a voltage that is lower than the second read voltage based on the number of off cells that are counted.