This paper reports a wet anisotropic etching process for the fabrication of silicon MEMS structures with rounded concave and sharp convex corners on (100)-Si wafers. The process is developed using tetramethyl ammonium hydroxide (TMAH) at different concentrations (10, 20, 25 wt%) and a small amount (0.1% v/v) of non-ionic surfactant NC-200. The etching characteristics are measured on a silicon hemisphere and several Si(100) wafers at 60 °C. The hemisphere is used to observe the etching behavior of different crystallographic planes. The present work aims at minimizing the etch rates of non-(100) planes, so that microstructures with rounded concave corners and convex corners can be realized easily. The proposed anisotropic wet etching is used for the fabrication of different kinds of microfluidic channels. Conformal etching in a single step can be realized for arbitrary mask designs targeting 20-25 μm deep microstructures.