A transistor amplifier package includes a base, one or more transistor dies on the base, first and second leads coupled to the one or more transistor dies and defining respective radio frequency (RF) signal paths, and an isolation structure on the base between the respective RF signal paths. The isolation structure includes first and second wire bonds. The first and second wire bonds may have a crossed configuration defining at least one cross point therebetween. Related wire bond-based isolation structures are also discussed.