Based on the quantum-confined Stark effect, a novel multimode interference 1×3 splitter incorporated with functions of electroabsorption modulator is proposed. The operating principle of the devices is analyzed in detail. On the basis of predefined ridge waveguide parameters which are length of 275 μm, width of 10 μm and thickness of 0.2 μm, a GaAs/AlGaAs multiple quantum well multimode interference 1×3 splitter is fabricated, coplanar waveguide structure is applied for electrode. The wave propagation characteristics of the splitter are numerically simulated by the finite difference beam propagation method and experimentally investigated. The static modulation characteristic of the device is also tested. When the applied direct current voltage is 3 V, Gauss beam with wavelength of 0.86 μm is symmetrically incident to the center of multimode waveguide, electroabsorption modulation depth is upto 90%, and bandwidth is 2 GHz.