The present invention relates to a capacitor in semiconductor device and a method of manufacturing the same, wherein, owing to formation of a lower electrode and an upper electrode into a stack structure of a poly-silicon layer and an aluminum (Al) layer and formation of an alumina (Al2O3) film as a dielectric film, the lower electrode is formed into a stack structure of the poly-silicon layer-aluminum (Al) layer, thus increasing a surface area of electrodes due to the absence of oxidation during annealing, and preventing degeneration of the device, and use of the dielectric film including a high-dielectric constant material layer enables reduction of the dielectric film's thickness. Accordingly, the present invention is capable of increasing capacitance, is capable of reducing leakage current and improving dielectric breakdown characteristics via internal formation of an MIM capacitor, and is capable of reducing production costs by performing a continuous process via use of a single piece of equipment.