An optical sensor includes a substrate and a light collimating layer. The substrate includes a sensor pixel array having a plurality of sensor pixels. The light collimating layer is disposed on the substrate. The light collimating layer includes a patterned seed layer, a plurality of transparent pillars, a metal layer, and a mask layer. The patterned seed layer is disposed on the substrate. The patterned seed layer exposes the sensor pixel array. The transparent pillars are disposed on the sensor pixel array. The metal layer is disposed on the patterned seed layer and in between the transparent pillars. The mask layer is disposed on the metal layer.