Provided is a PMOS resistor. The PMOS resistor includes a PMOS transistor pair, a switching unit, and a negative feedback unit. The PMOS transistor pair is symmetrically connected between first and second nodes. The switching unit compares a voltage of the first node and a voltage of the second node to output one of the voltages of the first and second nodes. The negative feedback unit receives an output of the switching unit to control a current which flows in the PMOS transistor pair, for maintaining a constant resistance value.