We have successfully grown thermodynamically stable ferromagnetic MnxGa1-x (x=0.55∼0.60) thin films with thicknesses ranging from 3 nm to 60 nm on GaAs substrates by molecular beam epitaxy. The c-axis of the tetragonal structure of the MnGa film is shown to be aligned perpendicular to the substrate. Both Magnetization Measurements and extraordinary Hall effect measurements indicate perpendicular magnetization of the MnGa films, exhibiting squarelike hysteresis characteristics. Furthermore, we have investigated the effect of Ni additions as a substitution for mn in (Mn60-yNiy) Ga40 alloy thin films with y=0 – 30 at% Ni. With increasing Ni, the perpendicular component of the magnetization becomes smaller up to y=18 where the magnetization is in-plane. At y=30, the magnetization is again perpendicular.