In this letter, we report a cascaded surfaceilluminated Germanium-on-Silicon (Ge-on-Si) avalanche photodiode (APD) array with a low dark current. The photodetector array cascades seven Ge-on-Si APDs through interconnecting the charge regions to form photomultiplier tubesiPMTjC which increases the effective light absorption area compared to the single APD scheme. To the best of our knowledge, this is the first time that Ge-on-Si PMT has been reported. The optimum response of single-electrode (2 pixels) Ge-on-Si APD is 2.4 A/W with a dark current of 100 nA, and the optimum bandwidth is 52 MHz. PMT has a responsivity of approximately 3 times that of a singleelectrode Ge-on-Si APD for the same dark current (100 nA). With low dark current, our PMT has a better optical amplification effect than the parallel Ge-on-Si PD. We have also further tested the current tuning properties of the Ge-on-Si APD arrays with different applied Ge voltages. The test demonstrates the feasibility of cascading three-electrode APD arrays. A cascaded Ge-on-Si APD array with good photodetection properties at low-light conditions has been demonstrated which provides guidance for the design of large-scale Ge-on-Si APD arrays for light detection and ranging application.