We report on the wrinkle formation in a thin film produced by the sol-gel method. Through the relaxation of stress, which results from the removal of the solvent during the drying process, an isotropic wavy pattern is generated in the form of skeletal branches. The patterns have a dominant wavelength satisfying a relationship of three-fourths order of thickness. Densification of the gelated film is enhanced by an increase in the volumetric strain caused by the evaporation of the remaining solvent from the film. The number of skeletal branches and surface roughness increases as the annealing time progresses, without any change in the skeletal wavelength.