A CMOS power amplifier includes: a first MOS transistor connected between a first power terminal and a first output stage and having a gate connected to an input stage; a second MOS transistor connected between the first output stage and a ground and having a gate connected to the input stage; a switching circuit unit connecting or separating a feedback line between the input stage and the first output stage to select a linear amplifying operation or a non-linear amplifying operation; and a resistor formed at the feedback line between the input stage and the first output stage to determine a linear amplification gain when the feedback line is turned on.