US Patent 7123535 Semiconductor integrated circuit device

In a non-volatile phase change memory, information is recorded by utilizing a change in resistance of a phase change portion. When the phase change portion is allowed to generate Joule's heat and is held at a specific temperature, it goes into a state of a low resistance. When the gate voltage of a memory cell selection transistor QM is controlled to afford a low resistance state, the maximum amount of current applied to the phase change portion is limited by the application of a medium-state voltage to the control gate, thereby avoiding overheating of the phase change portion.