Silicone encapsulations are widely used in high-temperature electronic applications, providing excellent properties like thermal stability, high purity, and chemical resistance. However, silicone is susceptible to moisture-induced failures due to high moisture permeability. This study mainly focuses on improving the moisture ingression characteristics of the silicone encapsulation by adding a polyurethane moisture barrier layer. This study focuses on the effects of moisture ingression by adding polyurethane and testing with embedded relative humidity sensors at different environmental conditions. The diffusivity of both the bi-layered composites and the pure encapsulation materials was assessed using two distinct experimental methods for the calculation of diffusivity based on the principles of 1-dimensional Fick's law of diffusion. The diffusivities were statistically analyzed to determine significant differences between the samples, and the experiment yielded a minimum of 65% reduction in diffusivity across the samples. Furthermore, a thermomechanical analysis was performed on two different GaN power MOSFETs by the application of different underfill and potting encapsulations to determine stresses and strains on the solder bumps.