A new structure integrated power amplifier with watt-level output power is presented in a standard 0.18μm CMOS process for WiMAX applications. A parallel cascode class A&B power amplifier with optimized widths is proposed to increase linearity and efficiency simultaneously. A novel interleaved PCT power combiner is proposed for increasing output power that combines output current of two similar class A&B power amplifiers. Proposed interleaved transformer heightens coupling factor compared to typical transformer.The proposed power amplifier with 3.3V power supply provides maximum output power of 32.5dBm and power added efficiency of 37.9% at 2.4GHz operating frequency. The proposed power amplifier exhibits high output power of 32.3dBm at 1dB compression point. The simulation results for proposed PA with modulated OFDM signal show that −31dB error vector magnitude at the average power of 25dBm can be achieved.