This paper presents a Class-D outphasing RF Power Amplifier (PA) which can operate at a 5.5V supply and deliver +32dBm at 1.85 GHz in a standard 130nm CMOS technology. The PA utilizes four on-chip transformers to combine the outputs of eight Class-D stages. The Class-D stages utilize a cascode configuration, driven by an AC-coupled low-voltage driver, to allow a 5.5 V supply in the 1.2/2.5 V 130nm process without excessive device voltage stress. Spectral and modulation requirements were met when a WCDMA and an LTE signal (20 MHz, 16-QAM) were applied to the outphasing PA. At +28.0 dBm channel power for the WCDMA signal, the measured ACLR at 5 MHz and 10 MHz offset were -38.7 dBc and -47.0 dBc, respectively. At +24.9 dBm channel power for the LTE signal, the measured ACLR at 20MHz offset was -34.9 dBc. To the authors' best knowledge, the PA presented in this work has a 3.9 dB higher output power compared to published CMOS Class-D RF PAs.