A method of manufacturing an optical sensor includes providing a semiconductor wafer including a plurality of pixel areas, providing a light transmissive substrate including a light transmissive wafer with a plurality of light transmissive members attached thereto, the plurality of light transmissive members being arranged on a first main surface of the light transmissive wafer and each of plurality of light transmissive members emitting α rays, an amount of the α rays being smaller than or equal to 0.05 c/cm2·h, fixing the light transmissive substrate onto the semiconductor wafer together by a fixing member, and dividing the semiconductor wafer and the light transmissive substrate that are fixed together into individual pieces.