Non-volatile semiconductor memory using a thin film transistor

A semiconductor device, comprising:

• an insulating gate transistor serving as a memory cell having a floating gate and a control gate wherein one end of a current path of said insulating gate transistor is connected to a bit line and another end is connected to a power source, and said control gate is connected to a word line;
• and
• a transistor including said control gate and said floating gate wherein said control gate is formed of a thin film, a portion corresponding to said floating gate is a channel region having an impurity concentration, which is lower than that of other portions of said control gate, said floating gate is a gate electrode controlling said channel region, a threshold voltage of said transistor of said memory cell, in which an electron is injected in said floating gate, increases and said transistor is set to be in an off state, said threshold voltage of said transistor of said memory cell, in which the electron is emitted from said floating gate, decreases and said thin film transistor is set to be in an on state, and if the voltage of said control gate increases in a reading operation, the high voltage of said control gate is supplied to a channel region of the on-state transistor, and said insulating gate transistor is turned on.