We report an on-chip high-speed visible-band electro-optic modulator that can operate over the full visible spectrum of 400–700 nm, with a record low Vπ⋅L of 0.48, 0.25, and 0.17V⋅cm at red, green, and blue wavelengths of 630, 520, and 450 nm, respectively, and an operation bandwidth of >20GHz .