This communication describes the first one-compartment hydrogen peroxide semi-fuel cell as a micro-power source for miniaturized applications. This power source is inspired by taking advantage of the high energy content of metals and design flexibility, light weight and ease of packaging. Benefiting from oxidation of metals, including magnesium (Mg) or aluminum (Al), at the anode and reduction of hydrogen peroxide (H2O2) at the cathode, theoretical specific energies of 8600 Wh kg-1 and 17000 Wh kg-1are achievable. Fabricating a cell with Mg as the anode and Prussian blue (PB) as the cathode, an open-circuit potential of 2.3 V with the net maximum power density of 7.5 mW cm-2 were achieved. These results are the highest ever reported for one-compartment H2O2-based power source. This cell design can provide a platform for fabrication of a new generation of power sources for portable and miniaturized applications.