A high-sensitivity optical sensor based on a Fabry–Pérot interferometer (FPI) has been demonstrated. The cavity of the FPI is formed by two parallel half-reflective film-coated glass substrates with a distance of 1 mm and works as the sensing area. The interaction between the propagating wave and the analyte gives the sensing signal. High sensitivity of 1149  nm  /  RIU has been achieved for the wavelength interrogation. The Fabry–Pérot sensor can be made into a large array with multiple microfluidic channels to detect the different types of analytes. It has great potential in biochemical sensing.