This paper presents the limitations of the helium leak test when applied to typical MEMS packages. A novel closed-form expression is presented which allows the determination of the minimum cavity volume package that can be accurately tested using the helium leak test method in conjunction with a standard gross leak test. This expression can be used to find optimum test parameters for packages with cavity volumes greater than 2.6 × 10-3 cm3. Hermeticity testing using FTIR and Raman spectroscopy are considered as potential methods to overcome the limitations of the helium leak test method. © 2011 Springer-Verlag.