The measurement method includes operations of applying a first gate bias voltage to a gate terminal of a first transistor that is included in a radio frequency (RF) power amplifier during a direct current (DC) measurement period, wherein the first transistor operates in a linear operation mode during the DC measurement period; measuring a first drain-source voltage of the first transistor and a current flowing through the first transistor via a connection node during the DC measurement period; applying a second gate bias voltage and a drain bias voltage to a gate terminal and a drain terminal of a second transistor that is electrically connected to the first transistor via the connection node; and measuring a DC value of the second transistor via the connection node during the DC measurement period.