The role of metal-insulator-semiconductor structure derived space charge field in the tip vibration signal of electrostatic force microscopy was studied using boron doped Si tip and Pt film sputtered on Si substrate. The ohmic contact between the tip and the film was confirmed by current-voltage characterization. Then the tip was held at a position so that an air gap of 100 nm existed between the tip and the film. The tip deflection and the tip vibration signals were examined by applying de voltage to the film and ac voltage to the tip. The asymmetry in both signals supports the existence of the space charge field, and the direction of the field at zero de bias field is from the tip to the sample as expected from the band bending theory.