In this work, we present a chip-integrated amperometric sensor targeted at the detection of hydrogen peroxide (H2O2) in the gaseous phase. Electrode chips are manufactured in a series of microfabrication steps and characterized electrochemically. Using such devices detection of H2O2 in an aqueous phase is shown by means of cyclic voltammetry and amperometry. Furthermore, it is discussed that variation of conditions such as the composition of the supporting electrolyte largely influences the obtained electrochemical signal. Additionally, electrochemical pretreatment of platinum working electrodes aiming at surface oxidation improves the limit of detection of the sensor and the linearity of the calibration curve at low H2O2 concentrations (<10 mu M). Agarose-coated electrode chips are used for the measurement of H2O2 in the gaseous phase. Detection of H2O2 is shown in a static and in a flow-through setup. We find a limit of detection of approximately 42 ppb. Current work focuses on expanding the presented device to detection of H2O2 in exhaled breath condensate.