A quadrature phase-shift keying (QPSK) coherent photodetector chip consisting of a $4\times 4$ multimode interference 90° optical hybrid and a four-channel evanescent photodetector array is designed and fabricated with its photo-response in the L-band characterized. The metal organic chemical vapor deposition regrowth method is adopted to realize active–passive monolithic integration. The chip exhibits a low dark current below 100 nA for each photodetector in the array, a low excess loss of 0.85 dB, a common mode ratio rejection better than 13.6 dB, and a phase deviation within $\pm 10°$ over the 40 nm wavelength span.