This paper presents a large-signal envelope-tracking (ET) polar transmitter (TX) system with a monolithic cascode SiGe power amplifier (PA) for mobile WiMAX applications. The envelope amplifiers are designed in the TSMC 0.35μm SiGe BiCMOS technology and also with discrete components for comparisons. The entire polar TX system using the discrete envelope amplifier in measurement achieves the power-added efficiency (PAE) of 30% at the average output power of 18 dBm with the EVM of 5% for WiMAX 64QAM 10 MHz signal. The RF/analog/digital co-simulations of the entire polar TX system with the integrated CMOS envelope amplifier show similar linearity and efficiency performances when compared with the measurement results. Both the simulation and measurement data suggests our polar TX design achieves the highest PAE among the state-of-the-art Si-based OFDM polar TX systems reported in the literature.