An optical sensor package comprises: a base substrate having a window; a first optical sensor mounted on a front surface of the base substrate, with its light receiving surface facing towards and aligned with the window; a first light-pervious encapsulant mold covering the light receiving surface of the first optical sensor; a first encapsulant layer formed on the front surface of the base substrate, wherein the first encapsulant layer comprises interlayer connects passing therethrough; an interposer mounted on the first encapsulant layer and electrically coupled to the base substrate through the interlayer connects of the first encapsulant layer; a second optical sensor mounted on a front surface of the interposer, with its light receiving surface facing away from the interposer; a second light-pervious encapsulant mold covering the light receiving surface of the second optical sensor; and a second encapsulant layer formed on the front surface of the interposer.