Air stability of C60 based n-type OFETs was investigated. At ambient conditions, the unencapsulated OFETs show rapid degradation in source-drain currents. In order to study the effects of encapsulation layers on air stability, the OFETs were encapsulated with singlesingle layers and bilayers. The OFETs protected by bilayer encapsulation show better air stability as compared to a single layer encapsulation. It has been found, that the barrier performance of the encapsulation layer can be improved by decreasing the surface roughness of the encapsulation layer. Our proposed encapsulation layers for n-type OFETs are transparent and flexible. Therefore, it can be used to encapsulate all type of organic semiconductor based devices also on plastic substrates for flexible devices.