Example apparatus and methods are disclosed. In one example, a memory device can include a memory array and a peripheral circuit. The memory array including a first memory string comprising a first select gate transistor and memory cells stacked vertically. The peripheral circuit coupled to the first select gate transistor via a select line and to the memory cells via word lines. The peripheral circuit is configured to apply a program voltage to a first word line and apply a first voltage to the select line during a time period of a first program operation, and apply a program voltage to a second word line and apply a second voltage to the select line during a time period of a second program operation. The second word line is farther from the select line than the first line and the second voltage is higher than the first voltage.