Normal-incidence p-i-n Ge/Si photodetectors were fabricated on SOI substrate by selective epitaxy. Thermal annealing and surface Si passivation were performed in situ to reduce the dark current. Bulk leakage current density and surface leakage density as low as 3.4 mA/cm² and 0.4 μA/cm are achieved under –1 V, respectively. The responsivity at wavelength of 1550 and 1310 nm are 0.27 and 0.59 A/W under zero-bias, respectively. The photodetector has a 3-dB bandwidth of 48 GHz at –3 V. Clear open eye diagrams at 40 Gbps are observed under zero-bias at a wavelength of 1550 nm.