We have successfully grown MnAs/ZnSnAs2/ZnSnAs2:Mn trilayer heterostructures on InP(001) substrates by molecular beam epitaxy. The magnetization curve showed small double steps due to the difference in coercive force between the ferromagnetic MnAs and ZnSnAs2:Mn layers. The current-in-plane giant magnetoresistance was clearly observed in magnetoresistance (MR) measurements in current-in-plane geometry. The MR ratio was found to be two times higher than that of single MnAs layer. This enhanced MR ratio can be ascribed to the GMR behavior in the trilayers, resulting from the change of the magnetization of the two ferromagnetic layers between parallel and antiparallel configuration. The temperature dependence of MR ratios also differ between the samples of trilayer and MnAs single layer.