The photoluminescence excitation spectra of AlxGa1−xP alloys withx=0–0.8 were measured at temperatures between 20 and 145 K. The crystals used in this study were prepared by slow cooling from the Ga‐rich Al‐Ga‐P solution. Two sharp lines,LandH, were observed at 2.305 and 2.314 eV at 80 K. TheHline is identified with theAline in GaP, which is due to the N isoelectronic impurity bound exciton. TheHline reduced drastically when a small amount of Al was added to the initial solution. This is because the presence of Al in the solution increases the difficulty of nitrogen being introduced into the crystal. The photon energy corresponding to theLline shows that this line is due to the donor bound exciton. The threshold point energyE0and theLline hardly change untilx=0.4; abovex=0.4 the energyE0begins to increase and theLline disappears. It is proposed that small clusters of GaP are formed in the AlxGa1−xP alloy because of a disordered arrangement of the group‐III atoms in the sublattice. The size of a cluster is thought to be larger than the exciton radius of 29 A˚ estimated by the hydrogenlike model.