Time‐resolved photoluminescence spectra and decay data are presented for a series of type II (GaAs/AlAs) samples with different GaAs layer thicknesses. Low‐temperature delayed spectra reveal that the spectral lines shift gradually to lower energy with delay, and that the shift extends to ms time scales. At 6 K the decay curves of the type II emission contain power‐law and exponential components with rates ∼103s−1, indicating significant Γ–Xmixing, both by random and nonrandom processes. Both rates increase with temperature. The dependence of the decay rates and spectra on the GaAs layer thickness is examined. Models of the recombination mechanisms are discussed in the context of these new results.