Disclosed are a semiconductor device and an operating method thereof. The semiconductor device includes a plurality of memory blocks including cell strings coupled between bit lines and a source line, a peripheral circuit configured to perform an erase operation on a selected memory block among the plurality of memory blocks; and a control circuit configured to control the peripheral circuit, so that when an erase command is received, local word lines coupled to a non-selected memory block among the plurality of memory blocks are pulled to ground, the local word lines coupled to the non-selected memory block float after a pre-erase voltage lower than an erase voltage is applied to the source line, and the erase operation of the selected memory block is performed by applying the erase voltage to the source line.