A 2.4/5.2 GHz CMOS dual band driver stages with integrated 5.2 GHz power amplifier is presented in this work. For more accurate simulation of high power CMOS amplifier, a re-optimized macro NMOS model is used, whose nonlinear model accuracy is enhanced and its validity is proved by comparing load pull simulation with measurement. In order to achieve band selection, it has switched matching circuits at the first stage and SPDT path switch following them. At 2.4 GHz and 5.2 GHz bands, the achieved values of Psat of the switched amplifier are 9.7 dBm and 19.5 dBm, respectively. The achieved PAE is 15.3% at 5.2 GHz.