A reference voltage circuit is provided. The reference voltage circuit includes a first current bias circuit including a first node; a second current bias circuit including a plurality of NMOS transistors and a second node, and an amplifier configured to output a reference voltage having same value as the second voltage. The plurality of NMOS transistors include a first NMOS transistor and a second NMOS transistor, the first NMOS transistor is connected to the first node, and the plurality of NMOS transistors are connected to the second node and configured to perform a sub-threshold operation based on a first voltage of the first node so that a second voltage is generated at the second node.