We have developed an easy fabrication method of Si field effect transistors (FETs) with poly (methyl methacrylate) (PMMA) gate films for science education. In this process, we can easily fabricate the silicon FETs only by means of metal deposition and thermal diffusion without any lithography processes. The organic isolation films of PMMA can be deposited by casting or painting at room temperature in air. The metal-organic-semiconductor FETs with PMMA exhibited almost the same drain current — gate voltage characteristics as those of conventional Si metal-oxide-semiconductor FETs, which are suitable for the education material of semiconductor engineering. The organic gate Si FETs can be used not only for education but also as thin film transistors for active matrix displays.