A light source device includes a substrate, an electrode layer and an annular step-like surrounding frame both disposed on the substrate, a light emitter and a light detector both spaced apart from each other and mounted on the electrode layer in the surrounding frame, and a light permeable member disposed on the surrounding frame. The surrounding frame includes an upper tread arranged away from the substrate, an upper riser connected to an inner edge of the upper tread, a lower tread arranged at an inner side of the upper riser, and a lower riser connected to an inner edge of the lower tread and arranged away from the upper tread. The surrounding frame has a notch recessed in the lower tread and the lower riser for spatially communicating an inner side of the surrounding frame to an external space.