We demonstrate the fabrication and characterization of single electron transistors composed of Au nanoparticles and insulating molecular tunnel barriers. We fabricated these devices by forming a 1,8-octanedithiol self-assembled monolayer on Au nanogap electrode pairs and by bridging them with colloidal An nanoparticles using ac dielectrophoresis. We observed the typical characteristics of these single electron transistors at the temperature from 4.2 to 300 K. The measured data were consistent with the orthodox theory of Coulomb blockade. (c) 2006 American Vacuum Society.