Disclosed herein are a perfluoroalkyleneoxy group-substituted phenylethylsilane compound and a polymer thereof. The perfluoroalkyleneoxy group-substituted phenylethylsilane compound represented by Formula 1 has excellent thermal and chemical stability to be solution-processed in a monomer state, and the polymer prepared by thermally crosslinking the compound has a high resistance to organic solvents. Moreover, since an insulating layer prepared by applying the same shows improved thermal and physical properties, it is possible to manufacture organic thin-film transistors having a high on/off ratio in a simple process such as a photolithography for a large-size substrate: ##STR00001## wherein R.sub.1, R.sub.2, R.sub.3, Z.sub.1, Z.sub.2, Z.sub.3, and n are the same as defined in the detailed description of the invention.