An electrically alterable read only memory with polysilicon gate is experimently realized employing a SONOS structure. The SONOS memory cells are proposed to achieve lower programming voltage with thin nitride (70A, 170$AA$) layer. Its programming voltage is 10V (Tnit=70$AA$), 22V(Tnit=170$AA$). And the SONOS cell is able to, erasc biasing negative gate pulse, then its voltage is about -24V for nitride thickness of 170$AA$.