A non-volatile semiconductor memory device includes a semiconductor substrate, a memory cell array formed on the semiconductor substrate, and including a first gate insulator having a first thickness. The measuring tube has, a smaller flow cross section than a supply segment of the process line connected to the inlet end of the measuring system. As a result, a reference voltage from the reference voltage generator is set to required voltage level, earlier than that from the sensing voltage generator. Common source lines are shared between only a pair of the neighboring word lines and are configured to electrically interconnect the common source regions with each other.