The test circuit monitoring positive bias temperature instability (PBTI) includes a PBTI monitoring unit driven according to a power voltage, the PBTI monitoring unit outputting an output voltage having a potential that is equal to or lower than a potential of the power voltage according to a PBTI degradation rate of an NMOS transistor; and a degradation determiner for determining the PBTI degradation rate by comparing the potential of the output voltage to the potential of the power voltage.