A non-volatile semiconductor memory device capable of reducing program disturb and a method of programming the same are provided. A bit line connected to a non-selected memory cell in the same block as a selected memory cell enters a floating state by inactivating a bit line selection switch, so that voltage levels of an first conductivity type channel and a source/drain terminal formed in a pocket second conductivity type well below a memory transistor have an intermediate level of a voltage level of a selection line and the pocket P type well. Therefore, program disturb caused by FN tunneling and junction hot electrons can be inhibited.