This paper presents some design insights on achieving a fully monolithic silicon-based radio frequency (RF) power amplifier (PA) using the envelope-tracking (ET) techniques for low-power broadband wireless applications. We will show that from our design experience, the highly integrated BiCMOS envelope-tracking power amplifier (ET-PA) system provides considerable efficiency-linearity enhancement, and works well with impressive power-saving for broadband 3G/4G cellular signals of high peak-to-average ratio (PAR). We will also demonstrate that further performance improvement of the fully monolithic BiCMOS ET-PA can be accomplished by: (1) combination of ET and transistor resizing techniques at the low output power regions; and (2) utilizing the ET technique with on-chip transformer power-combined SiGe PA for higher linear output power. For example, the fully monolithic BiCMOS ET-PA reaches the maximum linear output power (Pout) of 22.3/24.3 dBm with the overall power-added-efficiency (PAE) of 33%/42% at 2.4 GHz for the WiMAX 64QAM and the 3GPP LTE 16QAM modulations, respectively, without needing predistortion. Additionally, it can exhibit a highly efficient broadband characteristic for potential multi-band applications.