This paper presents the design of a high efficiency, 950 MHz fully differential power amplifier for wireless communications in a standard 0.18 μm CMOS technology. The power amplifier employs a fully differential class-E topology to achieve high power efficiency by exploiting its soft-switching property. The concept of mode locking is used in the design, in which the amplifier acts as an oscillator whose output is forced to run at the input frequency. The proposed power amplifier can deliver 23.5 dBm output power to a 50Ω load at 950 MHz with 41% power-added efficiency (PAE) from 1.8 V supply voltage.