We present a four-channel polarization-insensitive silicon photonic (SiPh) wavelength division multiplexing (WDM) receiver, incorporating a polarization splitting grating coupler, dual-ring filters and bidirectional photodiodes. This design achieves an ultra-compact footprint of 1 mm × 0.2 mm with a polarization dependent loss (PDL) of 0.58 dB or less. Four clearly open eye diagrams at a data rate of 112 Gb/s PAM4 are obtained. Furthermore, we demonstrate the hybrid integration of the SiPh chip with a 28 nm CMOS transimpedence amplifier (TIA), resulting in an impressive energy efficiency of 1.34 pJ/bit at a data rate of 100 Gb/s PAM4. Sensitivities of -13.4 dBm and -5.6 dBm are achieved at data rates of 50 Gb/s NRZ and 100 Gb/s PAM4, respectively, under KP4 forward error correction (FEC) threshold. © 1983-2012 IEEE.