This paper presents a 915MHz band ultra-low-power receiver with high energy efficiency for IoT applications. With the proposed polar receiver topology, the received Star- 16QAM signal is split into an ASK signal and D8PSK signal. A phase-tracking loop working as a phase domain ADC is adopted to demodulate the D8PSK signal, while the ASK signal can be demodulated by using a mixer-based energy detector chain. The receiver was designed and simulated in 65nm CMOS technology. Under 1V supply voltage, the power consumption of 445 μ W and the energy efficiency of 110pJ/bit have been achieved, which is at least 3.5× and 7.1 × better than prior arts, respectively. The simulated sensitivity is -76dBm at a data rate of 4Mbps. The figure of merit (FoM) of the receiver is 176dB.