A non-volatile memory of a complementary type includes sectors of memory cells, with each cell formed by a direct memory cell and a complementary memory cell. Each sector of the non-volatile memory is in a non-written condition when the corresponding memory cells are in equal states and is in a written condition wherein each location thereof stores a first logic value or a second logic value when the memory cells of the location are in a first combination of different states or in a second combination of different states, respectively. A sector is selected and a determination is made as to a number of memory cells in the programmed state and a number of memory cells in the erased state. From this information, the condition of the selected sector is identified from a comparison between the number of memory cells in the programmed state and the number of memory cells in the erased state.