In order to shorten initialization time, a flash type non-volatile semiconductor memory of the invention comprises a line decoder (2) for selecting all of word lines (WL1 to WLm), a word line voltage generator (3) for generating various voltage, a column decoder (4) for selecting or not selecting all of digit lines (DL1 to DLn). Erase pulse impression process is performed by supplying a positive first word line voltage to all the word lines (WL1 to WLm) selected, and an erase voltage (Vs) to a source line, leaving all the digit line floating. All of memory-cell-transistors (MC11 to MCmn) are erased by infusing hot carriers in their floating gates by way of avalanche breakdown caused between their sources and substrates. Depression discrimination is performed with a sense amplifier (8) by selecting all digit lines (DL1 to DLn) and supplying all word lines (WL1 to WLm) with a second word line voltage.