Theoretical and experimental results are reported on electro‐optical switching in a GaAs‐based multiple quantum well coupled planar nonlinear optical directional coupler. It is shown that a careful selection of the wavelength of operation can lead to an efficient, practically constant loss, low electric field controlled transfer of light energy from one slab waveguide to the other. The quantum‐confined Stark effect in the multiple quantum well coupling layer is employed as the switching mechanism. Results are compared with those achieved with nonlinear all‐optical switching in the same structure. It is believed that this is the first semiconductor &Dgr;Kswitch.