A semiconductor plastic package, more particularly a preferred package structure and method for making a BGA package. A resin sealed BGA package where a supporting frame which fixedly supports semiconductor parts; i.e., an IC chip, a circuit board, or a circuit film, is sealed with resin, using a mold which is composed of an upper mold half and a lower mold half with the lower mold half having a plurality of projections, one at a position corresponding to each of the external terminals. The mold has a divisional structure which has an air vent between the divisional elements thereof.