One or more embodiments are directed to system in package (SiP) for optical devices, such as proximity sensing or optical ranging devices. One embodiment is directed to an optical sensor package that includes a substrate, a sensor die coupled to the substrate, a light-emitting device coupled to the substrate, and a cap. The cap is positioned around side surfaces of the sensor die and covers at least a portion of the substrate. The cap includes first and second sidewalls, an inner wall having first and second side surfaces and a mounting surface, and a cover in contact with the first and second sidewalls and the inner wall. The first and second side surfaces are transverse to the mounting surface, and the inner wall includes an opening extending into the inner wall from the mounting surface. A first adhesive material is provided on the sensor die and at least partially within the opening, and secures the inner wall to the sensor die.