An apparatus and a method for packaging semiconductor devices. The apparatus includes a substrate strip component of a leadless three-dimensional stackable semiconductor package having mounting contacts on, for example, four peripheral edges. The substrate strip may either be fabricated for mounting a single electrical component (e.g., an integrated circuit die) or a plurality of substrate strips may be laid out in an X-Y matrix pattern which may later be singulated into individual package strip for leadless packages. Three-dimensional stacking is achieved by a bonding area on an uppermost portion of the sidewall. The sidewall of the strip is high enough to enclose an encapsulant covering a later mounted integrated circuit die and associated bonding wires.