Semiconductor memory device and operating method thereof

The invention relates to a semiconductor memory device and an operating method thereof. A semiconductor memory device includes: a memory block including a plurality of memory cells programmed to a plurality of program states during a program operation; a voltage generator configured to generate and apply a program voltage and a select line voltage to the memory block during a program operation; and a read/write circuit configured to temporarily store program data during a program operation, and control a potential of a bit line of the memory block based on the temporarily stored program data. The voltage generator generates the selection line voltage as a first selection line voltage during a first program operation for some of the plurality of program states, and generates the selection line voltage as a second selection line voltage during a second program operation for the remaining of the plurality of program states, a potential of the second selection line voltage is lower than a potential of the first s