A process for protecting a MEMS device used in a UV illuminated application from damage due to a photochemical activation between the UV flux and package gas constituents, formed from the out-gassing of various lubricants and passivants put in the device package to prevent sticking of the MEMS device's moving parts. This process coats the exposed surfaces of the MEMS device and package's optical window surfaces with a metal-halide film to eliminate this photochemical activation and therefore significantly extend the reliability and lifetime of the MEMS device.