Abstract: Background and Objective: Light capturing is an essential part of many optical devices such as optoelectronic devises and solar cells. This study aimed at modifying surface reflectivity of silicon to improve light trapping. A simple and easily controllable etching technique was used to achieve this goal. Methodology: The surface topography of (100) P-type silicon wafers was modified by etching a controllable pyramid structure on these surfaces. Potassium hydroxide (KOH) solution was used to etch the silicon surface; the concentrations of KOH were varied between (20-36 wt%)±0.14 wt% with 3±0.1 wt% of isopropyl alcohol (IPA) at temperatures between (60-80°C) ±0.1°C and a varying etching time between 20-40 min, the mean and standard deviation of the pyramids size was calculated by taking five SEM images per case. Results: The optimal etching condition was determined as a 20±0.14 wt% aqueous KOH solution with a 3±0.1 wt% IPA for an etching time of 40 min at an etching bath temperature of 80°C. The pyramids resulting under this condition has a size of 1.7±0.2 μm. The surface reflectivity at these optimal conditions was measured to be 11±0.2% in the wavelength range 550-840 nm. Conclusion: The optical conditions for etching and modifying the morphology and reflectivity of (100) silicon surfaces were determined. Surface reflectivity modification is one the effective methods that can be used to control light trapping and light scattering needed for proper functioning of many optical applications and optical devices.