Dependency of the surface hardness on the baking temperature of the resist film is studied. By using a micro-tip mounted in an atomic force microscope, the surface hardened layer of the resist film can be detected. On the other hand, knoop hardness measurement has no sensitivity to the surface hardness. The adsorption force of the atomic force microscope micro-tip has no correlation to the surface free energy of the resist film. The hardness behavior is affected by the solvent evaporation from the resist film. These results can be explained by the indentation model which contains the elastic deformation of the resist surface.