An input-output (I/O) receiver includes a receiving terminal, a first N-type metal-oxide-semiconductor (NMOS) transistor, a reformation circuit, and a compensation unit. The receiving terminal is coupled with an external voltage signal. The first NMOS transistor has a source electrode coupled with the receiving terminal and a gate electrode coupled with a first power supply voltage. The reformation circuit is configured to reform a voltage signal transmitted from a drain electrode of the first NMOS transistor. The compensation unit includes a first PMOS transistor, a second PMOS transistor, and a second NMOS transistor. Moreover, the compensation unit is configured to provide a compensation voltage to a voltage signal at the drain electrode of the first NMOS transistor thereby a maximum level of the voltage signal at the drain electrode of the first NMOS transistor reaches the first power supply voltage.