Ethylene-bridged silsesquioxane resins were synthesized from two monomers: 1,2-bis(trimethoxysilyl)ethane and methyltrimethoxysilane. The silsesquioxane thin films were spin-coated from the copolymerized resins on silicon wafer. Metal insulator metal (MIM), metal insulator semiconductor (MIS) devices were utilized to investigate the electrical properties of the copolymerized thin films. As the films were inserted as gate insulator in the OTFT devices, the field effect mobilitites were evaluated by employing Poly(3-hexylthiophene) (P3HT) as organic semiconductor, which shows that their dielectric properties and mobility values are dependent on the molecular structures and Si-OH concentration involving in the films.