Abstract: A package structure for horizontal cavity surface emitting laser diode with monitor photodiode chip includes a header with a plurality of conductive pins, where three conductive pins extend onto the surface of the header. One of the conductive pins is attached to a stage with a slope and a monitor photodiode chip is placed on the top of the stage. A submount is placed among the three conductive pins and is attached to a laser diode chip. The back facet of the laser diode chip is facing the stage. The upward surface emission light of the laser diode chip is focused outside the transparent window by the lens on the transparent window and the horizontal emission light of the laser diode chip is incident on the monitor photodiode chip, whereby the power of the light can be detected.