End-grafted polystyrene, "brushes" of various thickness and grafting density on silica surfaces were synthesized by surface-initiated polymerization. The "brushes" were studied by contact angle measurements, ellipsometry, and scanning force microscopy (SFM). Wetting behavior of thin polystyrene film on the top of the grafted layers was investigated using optical microscopy and SFM. The film stability was strongly dependent on the grafting amount. We identified three grafting density regimes with respect to stability of the top polystyrene films: at small and very large grafting density the top film dewets "brushes". while at moderate grafting density the polystyrene film was stable after 80 h of annealing time at 155 degreesC.