Components Expiration date
Semiconductor parts I buy from Future sometimes come in hermetically-sealed antistatic bags, with silica gel inside. 

Each come with a warning about humidity. (I will try to find one.) I believe the warning is parts should be used within six months once the package is opened. 

I believe the issue is not about the silicon deteriorating. It is about moisture being absorbed by the package which may cause failure during the surface mount soldering process.

I have no reason to believe it is unique to the parts I buy from Future, and may apply to other parts with similar package properties.