© The Electrochemical Society. This work describes the recent researches on bacterial sensing using microelectromechanical systems (MEMS) technology. The fluorescent characteristics for one of the targeting bacteria, Legionella pneumophila (L. pneumophila) cells trapped in a bio-MEMS microfluidic chip were first studied, showing they emit blue fluorescence when they are forced to stop their motion. The ultraviolet (UV) photoirradiation time dependences of fluorescent spectra were further compared between L. pneumophila and L. dumoffii. The photocurrent of fluorescence from L. dumqffii confined in the bio-MEMS microfluidic chip were able to be measured by a photogate-type Si photodetector. These results indicate that the combination of the Si photodetector with bio-MEMS microfluidic chip enables to make bacterial sensors for Legionella on a chip.