A semiconductor device has a floating gate structure in which charge storage layers are stacked on a SiO2 layer formed on a substrate made of n-type Si. The charge storage layer has quantum dots made of undoped Si and an oxide layer that covers the quantum dots. The charge storage layer has quantum dots made of n+-Si and an oxide layer that covers the quantum dots. Electrons originally existing in the quantum dots migrate between the quantum dots and the quantum dots via tunnel junction and are distributed in the quantum dots and/or the quantum dots according to the voltage applied to a gate electrode via pads. The distribution is detected in the form of a current (ISD).