GaNAs/GaP strained single quantum wells are fabricated on GaP wafers by gas-source molecular beam epitaxy in which a nitrogen radical is used as the nitrogen source. The structure and luminescence properties of the quantum wells are investigated by transmission electron microscopy and photoluminescence measurements. The N content in the GaNAs quantum wells was estimated to be about 10%, which is about one order of magnitude larger than previously reported and more than sufficient for fabricating laser diodes on a Si wafer.