A time‐resolved pump‐probe configuration employing 10 ps laser pulses has been used to investigate the all‐optical switching characteristics of zero‐gap directional couplers containing a single quantum well. All‐optical switching of the weak probe pulses from one port into the adjacent one was obtained at pump input pulse energies of 150 pJ. The switching takes place within the duration of the laser pump pulses. The recovery time of the device was found to be ∼1.5 ns which indicates that carrier diffusion plays a major role in the device switching speed.