A manufacturing method of a semiconductor device in which the threshold is adjusted is provided. In a semiconductor device including a plurality of transistors arranged in a matrix each including a semiconductor, a source or drain electrode electrically connected to the semiconductor, a gate electrode, and a charge trap layer between the gate electrode and the semiconductor, electrons are trapped in the charge trap layer by performing heat treatment and, simultaneously, keeping a potential of the gate electrode higher than that of the source or drain electrode for 1 second or more. By this process, the threshold increases and Icut decreases. A circuit that supplies a signal to the gate electrode (e.g., word line driver) is provided with a selection circuit formed of an OR gate, an XOR gate, or the like, whereby potentials of word lines can be simultaneously set higher than potentials of bit lines.