A semiconductor sensor is contained in a cylindrical housing, an opening of which is closed with a cover member. The cover member includes a mounting plate integrally molded therewith. Components including a bare sensing chip and other circuit chips are directly mounted on a flat surface of the mounting plate. The components mounted on the flat surface are covered with gel having a high flowability. The gel is prevented from flowing out of the flat surface toward the cover member by banks formed at both sides of the flat surface. On an inner wall of the bank, curved surfaces and depressions are formed to surely suppress creeping up of the gel and to trap the gel therein if it creeps up the inner wall of the bank. Thus, the gel is surely prevented from flowing out even though the banks do not entirely surround the flat mounting surface.