It has been shown earlier that GeSi/Si resonant‐cavity photodiodes can achieve high speed without sacrificing quantum efficiency. In this letter, we report a Si‐based resonant‐cavity photodiode that utilizes a Si/SiO2 Bragg reflector. This structure is more compatible with standard Si processing technology than the GeSi/Si resonant‐cavity photodiodes. The absorbing region is a 1‐μm‐thick polysilicon layer that has been annealed to enhance secondary grain growth and the bottom mirror consists of three quarter‐wavelength pairs of Si and SiO2. After annealing the dark current was 9 μA at 1 V, the peak quantum efficiency was 44%, and the bandwidth was ≳1.4 GHz.