InGaAs/GaAs strained‐layer superlattices have been grown by molecular beam epitaxy and characterized with photoconductivity measurements. The layers were dopedptype by diffusion of Zn in an ohmic contact annealing process. A sudden reduction in room‐temperature photoconductivity of thep‐type samples was observed at photon energies slightly below the GaAs band gap in all of the samples. This spectral feature is proposed to originate from photoionization of acceptor‐like defect states in GaAs, and a model accounting for this phenomenon is discussed.