A micro scale dc plasma discharge was studied to determine the potentialities for lab-on-the-chip applications. Different working conditions for the micro plasma discharge were considered: the pressure was varied between 2.7 and 5.3 kPa and the applied dc voltage was between 400 and 540 V, generating a discharge current in the range of 0.02–0.09 mA. The electrode distance was maintained at 0.025 cm and argon was used as the gas for the formation of plasma discharges. The number densities of excited states were determined by spectral emission data (400–1000 nm) and then were calculated by introducing a few assumptions: comparison of experimental and calculated number densities allowed an analysis of a volume averaged electron energy distribution function. Also, it was possible to estimate an effective electron temperature for different conditions of pressure and applied voltage.Copyright Institute of Physics 2004