Wet etching is an essential and complex step in semiconductor device processing. Metal-Assisted Chemical Etching (MacEtch) is fundamentally a wet but anisotropic etching method. In the MacEtch technique, there are still a number of unresolved challenges preventing the optimal fabrication of high-aspect-ratio semiconductor micro- and nanostructures, such as undesired etching, uncontrolled catalyst movement, non-uniformity and micro-porosity in the metal-free areas. Here, an optimized MacEtch process using a nanostructured Au catalyst is proposed for fabrication of Si high aspect ratio microstructures. The addition of isopropanol as surfactant in the HF-H2O2 water solution improves the uniformity and the control of the H2 gas release. An additional KOH etching removes eventually the unwanted nanowires left by the MacEtch through the nanoporous catalyst film. We demonstrate the benefits of the isopropanol addition for reducing the etching rate and the nanoporosity of etched structures with a monotonic decrease as a function of the isopropanol concentration.