The invention discloses a plastic cooler for semiconductor modules. The cooling apparatus includes a plurality of discrete modules and a plastic housing. Each module includes a semiconductor die encapsulated by a mold compound, a plurality of leads electrically connected to the semiconductor die and protruding out of the mold compound and a first cooling plate at least partly uncovered by the mold compound. The plastic housing surrounds the periphery of each module to form a multi-die module. The plastic housing includes a first singular plastic part which receives the modules and a second singular plastic part attached to a periphery of the first plastic part. The second plastic part has cutouts which expose the first cooling plates and a sealing structure containing a sealing material which forms a water-tight seal around the periphery of each module at a side of the modules with the first cooling plates.