In this paper, we present a broadband terahertz wave amplitude modulator based on optically-controlled gold-doped silicon. Gold dots with a diameter of 40 μm are used as a dopant source. Experimental results indicate that interstitial Au atoms provide effective recombination centers for photo-generated electron-hole pairs in Si body, leading to a significant decrease of the minority carrier lifetime from more than 10 μs to about 110 ns. Dynamic modulation measurement at 340 GHz carrier shows a modulation depth of 21% and a maximum modulation speed of 4.3 MHz. This modulator has advantages such as wideband operation, high modulation speed, polarization insensitivity, and easy manufacture by using the large-scale integrated technology, and thus can be widely used in terahertz technology.