Band gap energies of SrTiO$_3$(STO) thin film on glass substrates were studied in terms of annealing temperature. The STO thin film was fabricated by our newly developed method based on the combination of the Self-Assembled Monolayer(SAM) technique and the Liquid Phase Deposition(LPD) method. The as-deposited film demonstrated a direct band gap energy of about 3.65 eV, which further increased to 3.73 eV and 3.78 eV by annealing at 40$0^{circ}C$ and 50$0^{circ}C$, respectively. The band gap energy saturated at about 3.70 eV for the crystallized film which was obtained by annealing at 600-$700^{circ}C$. The relatively large band gap energies of our crystallized films were due to the presence of minor amorphous phase, grain boundaries and oxygen vacancies generated by annealing in air.