A semiconductor structure includes a memory array, a staircase unit, conductive bridge structures, a word line driver and conductive routings. The memory array is disposed in an array region of the semiconductor structure and includes word lines. The staircase unit is disposed in a staircase region and surrounded by the array region. The staircase unit includes first and second staircase steps extending from the word lines of the memory array. The first staircase steps and the second staircase steps face towards each other. The conductive bridge structures are electrically connecting the first staircase steps to the second staircase step. The word line driver is disposed below the memory array and the staircase unit, wherein a central portion of the word line driver is overlapped with a central portion of the staircase unit. The conductive routings extend from the first and the second staircase steps to the word line driver.