A light source device includes a package, one or more semiconductor lasers each having an emission surface, a light-transmissive cover, and an optical member. The package includes an inner bottom surface and inner lateral surfaces, and a recess defined by the inner bottom surface and the inner lateral surfaces and having an open end. The one or more semiconductor lasers are arranged on the inner bottom surface. The light-transmissive cover covers the open end of the recess. The optical member is arranged on an upper surface of the cover and is configured to mix light. The one or more semiconductor lasers are arranged so that their emission surfaces are respectively oblique to their adjacent inner lateral surface when viewed from above, and the inner lateral surface has a reflecting region arranged inclined with respect to the bottom surface.