The aim of this chapter is to present a short review in the field of design, fabrication technology, and testing of high-efficiency surface-barrier photodiodes with electrodes based on thin-film transparent conducting oxides (TCO) such as tin-doped indium oxide (ITO) and fluorine-doped tin oxide (FTO). Most of this review is based on our own results obtained and reported during the last 30 years. Besides a brief description of the low-cost spray pyrolysis deposition technique, mainly used in our work for deposition of the TCO films on a semiconductor surface, structural, morphological, and optoelectronic properties of these TCO films are discussed. As an example, a successful application of these TCO films is shown and used in high-efficiency surface-barrier photodiodes for a wide spectral range, from near ultraviolet (UV) to near infrared (NIR), and fabricated on different semiconductor substrates such as traditional Si, wide energy band ZnS, and GaP compound semiconductor substrates. The possible use of the Si surface-barrier structures as radiation-resistant detectors and gamma radiation detectors is discussed. The properties of high-efficiency surface-barrier photodiodes based on a perspective ternary semiconductor compound, Hg 3 In 2 Te 6 mercury indium telluride (MIT), for detection of 1.3 μm and 1.55 μm radiation for applications in fiber optics, are also reported.