For the development of micro gas sensors, studies of field ionization and break-down in small gaps were performed. A finite element simulation was done for an estimate of the achievable field strength near a nanotube tip in small gaps. The simulation also showed the relatively low importance of the gross electrode geometry when significant protrusions are present. For first measurements two types of test structures were fabricated: planar micro devices with thin film platinum electrodes, and a structure with nanotubes on silicon as electrodes. Both types showed characteristic conditioning behaviour and breakdown at voltages of expected magnitude.