The microstructure of the sputtered-YMnO3, thin films on Si (100) substrates was controlled by only using thermal treatment processes and YMnO3 thin films having a well-defined bi-layered microstructure were fabricated. These YMnO3 thin films have two distinct layers, i.e. approximately 40 nm-thick top layer of {00l}-oriented YMnO3, and approximately 60 nm-thick bottom layer of polycrystalline YMnO3 in the 100 rim-thick film. The abrupt change of the crystalline orientation from the {00l}-preferred orientation to the random orientation is mainly due to a high stress induced by die {00l}-oriented YMnO3 layer, which was confirmed by a full width at half-maximum in Si (004) rocking curves. The controlled c-axis/polycrystalline YMnO3 thin films showed a better memory window and low leakage current density than purely c-axis-oriented YMnO3 thin film and the purely polycrystalline YMnO3 thin film.