Abstract: Enantioselective enzyme FET for the detection of β-hydroxy acid esters and aromatic amino esters were prepared by immobilizing various enzymes on to the pH-sensitive gate surface of a pH-FET. Esterase was used for the unspecific hydrolysis of the substrate into the respective acid and alcohol and α-chymotrypsin and lipase were used for the enantiomeric specific hydrolysis of S-phenyl-alanine methyl ester and S-3-hydroxy-3-phenylpropanoic acid ethyl ester, respectively. The enzymes were immobilized by crosslinking with glutardialdehyde and human serum albumin. The biosensors and a Ag+/Ag reference electrode were mounted in a flow-through detector cell of a FIA system. The esterase-FET gave a linear response for up to 2 g/l of R,S-phenyl-alanine methyl ester and up to 1 g/l for R,S-3-hydroxy-3-phenylpropanoic acid ethyl ester. The α-chymotrypsin-FET and the lipase-FET gave linear responses for up to 2 g/l for S-phenyl-alanine methyl ester and 5 g/l of S-3-hydroxy-3-phenylpropanoic acid ethyl ester, respectively. The sensors gave a maximum signal at pH 8. The sensor signal exhibited good reproducibility (no details given) and the sensor life-time was >40 days.