a reference voltage generator includes a first transistor and a second transistor coupled in series between a current supply and ground . gate insulating films of the first transistor and the second transistor are made of the same type of film with the same thickness . impurities contained in gate electrodes of the first transistor and the second transistor have different conductivity types , or have the same conductivity type and different concentrations . the first transistor has a greater gate width than the second transistor . the first transistor and the second transistor operate in a subthreshold region when a reference voltage is output outside .