By using Au-nanorod (Au-NR) doped graphene as a transparent conducting electrode, Si-based metal-oxide-semiconductor (MOS) photodetectors (PDs) exhibit high external quantum efficiency (EQE) and fast response time. It is found that upon adding Au-NRs to the graphene, a significant increase in EQE is observed for both planar and Si-nanotip (Si-NT) MOS PDs. The planar Si-based MOS PDs reveal a notable photoresponse with an EQE of 49% at the peak wavelength of 530 nm under zero bias and an EQE of 66% at the peak wavelength of 600 nm under - 0.4 V bias. For the Si-NTs MOS PD, it exhibits a relatively high EQE of 71% under - 4 V bias due to the effect of light trapping arising from the nature of the Si-NT array.