The magnetization of the dilute magnetic alloy GaMnP:C prepared by the implantation of Mn into p-GaP:C or by direct molecular-beam epitaxy is reported. The material implanted to produce a Mn level of 3% produces ferromagnetic behavior that persists up to a temperature of 330 K, while the epitaxially derived material shows evidence of ferromagnetism at a temperature of 300 K. In both cases, no second phases were observed by x-ray diffraction, transmission electron microscopy, or selected area diffraction pattern analysis. A phase diagram of the GaMnP:C system, determined by epitaxial growth, is also reported.