An apparatus and method for molding balloon catheters is disclosed. The balloon may be molded by providing a polymeric tube within a mold having an interior cavity in the shape of the desired balloon. Microwave energy, which may be generated by a gyrotron, may then be directed toward the mold, to heat the polymeric material without heating the mold. Once heated, pressurized fluid may be injected into the tube to blow the polymeric material against the interior cavity whereupon the material can cool to form the balloon or can be further heatset by additional microwave energy and be cooled to form the balloon. In accordance with one embodiment, microwave energy can also be used without a mold to form a medical device.