Mn-doped ZnO (ZMO) semiconductor thin films were synthesized using a radio-frequency (RF) sputtering system, and p-type ZMO thin films were produced using only Ar working-pressure control at room temperature with no additional dopant. The carrier type and the density were confirmed using a Hall measurement system. The role of Mn ions in the p-type ZMO thin films was investigated using X-ray photoelectron spectroscopy (XPS). The p-type properties and the potential device applications were investigated through hetero p-n junction ZMO/Si diode operation. We improved the contact property between the electrode and the device material by using an isostatic pressure treatment under an Ar atmosphere.