One aspect of the invention pertains to a semiconductor package suitable for use in high stress environments, such as ones involving high pressures, temperatures and/or corrosive substances. In this aspect, a die and leadframe are fully encapsulated in a first plastic casing. The first plastic casing is fully encapsulated in turn with a second plastic casing. The two casings have different compositions. The first plastic casing, for example, may be made of a thermoset plastic material and the second plastic casing may be made of a thermoplastic material. The first plastic casing may have recesses, indentations and/or slots suitable for securing it to the second plastic casing. In some embodiments, a corrosion resistant coating is added to the second plastic casing. Methods for forming semiconductor packages suitable for use in high stress environments are also described.