The conduction‐band offset &Dgr;Ecof Al0.3Ga0.7As/In0.1Ga0.9As0.8P0.2lattice matched to a GaAs substrate was measured by capacitance‐voltage analysis. To examine the transitivity of the band offset in the AlGaAs/InGaP/InGaAsP system, the band offsets of Al0.3Ga0.7As/In0.5Ga0.5P and In0.5Ga0.5P/In0.1Ga0.9As0.8P0.2were investigated. The value of &Dgr;Ecfor the Al0.3Ga0.7As/In0.1Ga0.9As0.8P0.2heterostructure, estimated by adding the measured &Dgr;Ecvalues in Al0.3Ga0.7As/In0.5Ga0.5P and in In0.5Ga0.5P/In0.1Ga0.9As0.8P0.2, agrees well with the value measured directly. We thus conclude that the transitivity rule holds well for the band offsets of an AlGaAs/InGaP/InGaAsP system lattice matched to a GaAs substrate. ©1996 American Institute of Physics.