A miniature differential surface stress sensor consisting of two adjacent micromachined cantilevers (a sensing/reference pair) is developed for detection of chemical and biological species. Presence of analyte species is detected by measuring the differential surface stress associated with adsorption/absorption of chemical species on sensing cantilever. A novel interferometric technique is utilized to measure the differential surface stress induced bending of sensing cantilever with respect to reference cantilever. Sensor performance is characterized through measurement of surface stress associated with formation of alkanethiol self-assembled monolayers (SAMs) on gold coated sensing cantilever. Chemisorptions and self-assembly of alkanethiol molecules onto the gold-coated cantilever surface leads to development of compressive surface stress. Magnitude of measured surface stress compares well with data reported in literature.