Conventional RF power amplifiers are normally designed for peak efficiency at maximum output power. However, for WCDMA application, the power amplifier often operates at 6-8 dB power back-off. Consequently, when the power is backed-off from its peak point, the efficiency of conventional power amplifier drops sharply. The envelope elimination and restoration (EER) and envelope tracking (ET) systems are two of the most promising techniques that can provide high efficiency at power back-off point. In this project, a RF power amplifier optimized for average efficiency according to the PDF of WCDMA signal has been designed using NXP generation 7 LDMOS. In addition, to meet the increasing demand for wireless communication terminals to handle wideband operation, a 1GHz bandwidth power amplifier optimized for efficiency at power back-off has been designed and fabricated. The measurement results are proved to have a good agreement with simulation results.