Magnetization transition from in-plane to perpendicular caused by temperature changes was investigated for the magnetostatically coupled multilayer films (GdFeCo/AlN/DyFeCo). The results indicate that the magnetization orientation of the readout layer (GdFeCo) is affected by the saturation magnetization and the effective anisotropy energy, but the transition occurs mainly as a result of the change of the saturation magnetization. At high temperature the saturation magnetization and the demagnetizing energy of the GdFeCo layer decrease, then the transition of the GdFeCo layer from in-plane to perpendicular magnetization occurs due to the magnetostatically coupled interaction. The magnetization direction of the readout layer changes rapidly in a narrow temperature range.