The inorganic 20GeO(2)(2)(: 80SiO) (germanosilicate) thin films were prepared by sol-gel spin-coating and annealed at 700 and 900C. The densification and properties of the films were studied by varying the pH levels of the starting sol ranging from 1 to 6. The -OH content in the thin films was estimated by Fourier transform infrared spectroscopy. The porosity value was derived from the index (n) of the films as determined by spectroscopic ellipsometry and was used to evaluate the densification of the material. The minimum -OH stretching band was found to occur at pH 3 for samples annealed at 700 and 900C. For the film annealed at 900C, the -OH stretching band disappeared and zero porosity was obtained. Atomic force microscope images show fairly smooth film surface prepared at pH 3 and annealed at 900C. The noncrystallinity of the films was studied by means of X-ray diffraction and was confirmed by micro-Raman spectroscopy. This study leads to the development of a high-quality thin film. Iterative deposition of dense germanosilicate thin films was used to fabricate a 3 mm single-mode (at 1.55 mm wavelength) slab waveguide with a low propagation loss of 0.26 dB/cm. 2005 The Electrochemical Society. All rights reserved.