A semiconductor package including an organic interposer includes: a semiconductor chip; a connection member on the semiconductor chip and including a pad layer, a redistribution layer, and an insulating layer; a bonding member between the semiconductor chip and the pad layer; a surface treatment layer on the pad layer and including at least one metal layer; and an under-bump metallurgy (UBM) layer embedded in the connection member. The UBM layer includes a UBM pad, at least one plating layer on the UBM pad, and a UBM via. The surface treatment layer is disposed only on one surface of the pad layer, the plating layer are is disposed only on one surface of the UBM pad, and at least a portion of a side surface of the plating layer is spaced apart from a side surface of the insulating layer surrounding the plating layer.