Organic thin film transistors with improved mobility are disclosed. The transistor contains two interfacial layers between the dielectric layer and the semiconducting layer. One interfacial layer is formed from a siloxane polymer or silsesquioxane polymer. The other interfacial layer is formed from an alkyl-containing silane of Formula (1): where R′ is alkyl having from about 1 to about 24 carbon atoms; R″ is alkyl having from about 1 to about 24 carbon atoms, halogen, alkoxy, hydroxyl, or amino; L is halogen, oxygen, alkoxy, hydroxyl, or amino; k is 1 or 2; and m is 1 or 2.