Reference voltage generator having diode-connected depletion MOS transistors with same temperature coefficient

A reference voltage generator has a first N type depletion MOS transistor configured to cause a constant current to flow, and a second N type depletion MOS transistor diode-connected to the first N type depletion MOS transistor and configured to generate a reference voltage based on the constant current. The first and second N type depletion MOS transistors have the same temperature coefficient of a threshold voltage. The first N type depletion MOS transistor has a buried channel into which arsenic impurities are diffused. The second N type depletion MOS transistor has a buried channel into which phosphorous impurities are diffused.