A semiconductor sensor includes: a semiconductor substrate; a plurality of piezoelectric thin films layered on the semiconductor substrate, the plurality of piezoelectric thin films including at least a pair of the piezoelectric thin films layered above and below; a pair of electrodes that are formed at an interface of at least the pair of the piezoelectric thin films layered above and below and excite surface acoustic waves; a thin film directly under a lowest-layer piezoelectric film of the piezoelectric thin films; a metal thin film that is formed at an interface of the lowest-layer piezoelectric thin film and the thin film, and facilitate a growth of a ridge-and-valley portion on a surface of an uppermost-layer piezoelectric thin film of the piezoelectric thin films; and a sensitive film for molecular adsorption formed on at least the ridge-and-valley portion on the uppermost-layer piezoelectric thin film.