The method and conditions of Ni plating were optimized to maximize the output of a betavoltaic battery using radioactive63Ni. The difference of the short circuit currents between the pre- and postdeposition of63Ni on the PN junction was 90 nA at theI-Vcharacteristics. It is suspected that the beta rays emitted from63Ni did not deeply penetrate into the PN junction due to a Ni seed layer with a thickness of 500 Å. To increase the penetration of the beta rays, electroless Ni plating was carried out on the PN junction without a seed layer. To establish the electroless coating conditions for63Ni, nonradioactive Ni was deposited onto a Si wafer without flaws on the surface. This process can be applied for electroless Ni plating on a PN junction semiconductor using radioactive63Ni in further studies.