Praseodymium dioxide doped layers are grown on semi-insulating InP substrates with liquid-phase epitaxy. The quaternary layer composition determined with two-crystal X ray diffraction and photoreflectance is found to be independent of the PrO2 concentration in the melt. The photoluminescence spectra measured at 12K show both exciton and donor-acceptor peaks, the magnitudes of which depend on the PrO2 doping. The carrier concentration of the n-type quaternary layer decreases and the mobility increases with increasing PrO2 concentration and reaches the values of 8.3·1015 cm-3 and 7300 cm2/Vs, respectively, at about 0.1 wt% at 77K. The experiments show that PrO2 has an impurity gettering effect in the growth process.