The magnetic properties of a Cd1−xMnxGeAs2: MnAs hybrid micro-composite have the signature of ferromagnetic order at room temperature. Magnetotransport reveals the presence of a large linear positive magnetoresistance, with maximum values of about 550% (B=22 T) for x=0.028. This is interpreted in terms of an effective medium approximation with the value and the shape of the magnetoresistance depending on the structural and electronic properties of the semiconductor rather than on its magnetic properties. The absence of an anomalous Hall effect leads to the conclusion that ferromagnetic ordering is not the only factor necessary for the occurrence of asymmetric scattering in granular ferromagnetic materials.