The conduction-band discontinuity ΔEc of AlxGa1−xAs/In0.5Ga0.5P heterojunctions grown by liquid phase epitaxy on GaAs substrate was studied using the capacitance–voltage (C–V) characterization technique. The C–V measurements were made on a series of samples with x ranging from zero to about 0.3. The carrier profiles for the samples with x=0 and x=0.06 give ΔEc values of 90 and 40 meV, respectively, showing the type I (straddling) band line-up. For x=0.18 and 0.29, the values of ΔEc were 45 and 110 meV, respectively, with the carrier profile characteristic of the type II (staggered) band line-up. From these results, ΔEc of the heterojunction is found to vanish at about x = 0.12. This agrees well with our previous result determined from the photoluminescence measurements.