This work focuses on the etching characteristic of (100) silicon wafer in surfactant added tetramethyl-ammonium-hydroxide (TMAH:( CH3)4NOH) solution. The experimental result shows that under etching effect in TMAH achieves a significant reduction by adding fatty alcohol ethoxylate (R-O (CH2-CH2)n-OH) in the solution. Synperonic-A series fatty-alcohol-ethoxylate with increasing length of ethylene oxide segments are used to carry out the experiment. Comparing with the pure TMAH, the maximum under etching rate in the surfactant added TMAH is reduced to three quarters. The etching loss of convex corners is negligible for shallow to medium-deep etching (<30μm).