High-resolution analytical techniques based on scanned microprobes over surfaces are useful to investigate reactions at different materials in solution, with possibilities for remote sensing. One of these techniques is Scanning Electrochemical and Photoelectrochemical Microscopy (SPECM), which allows to investigate both electrochemical and photoelectrochemical reactions either concurrently or simultaneously over a semiconductor surface. SPECM is based on the use of an optical fiber coated with a noble metal and isolated from its surrounding media with a polymer film. Spatial resolution for this technique strongly depends on the characteristics of the probe, for instance numerical aperture or the characteristics of optical fiber tips. According to this, there is an increasing need for reducing the optical probe sizes, as well as the illumination spot size, in order to improve spatial resolution for this technique. Usually, optical scanning probes are prepared by chemically etching an optical fiber in HF solutions or by heating and stretching an optical fiber locally with an oscillating flame or a CO 2 laser beam. In this work, the goal of this study is to establish the optimal tip diameter and the total length of the taper in order to obtain a good transmission efficiency and thus to improve the sensitivity of the SPECM technique.