The photoresponse to a short optical pulse of a GaAsp‐njunction containing an undoped asymmetric GaAs/AlAs superlattice is reported. The response to a light pulse of <400 fs duration has been measured and a rise time of 80 ps is observed. The trailing edge of the response exhibits a long time tail, which is thought to be dominated by the time taken to tunnel through the thickest barrier, being the &Ggr;‐&Ggr; separation of the GaAs and AlAs of a 3‐nm barrier.