AbstractBand offsets can be found by high‐pressure spectroscopy if the X‐minima of a heterostructure are type II. However, many heterostructure systems do not have a type II X‐minimum and then this method does not work. We therefore propose a new approach to measuring band offsets. It is capable of obtaining the band offsets of any near‐GaAs alloy against GaAs by comparing the photoluminescence energies of alloy and GaAs quantum wells with AIGaAs barriers below and above crossover. The method is demonstrated for the case of InGaAs. There are other candidate systems which may usefully be used in the same manner as GaAs/AIGaAs. Before they can be used it is necessary to check whether the X‐minimum is type II or not. We present data confirming that the GaInP/GaAs system also has a type II X‐minimum and can therefore also be used.