Abstract: A design scheme of microbattery with semiconductor material GaAs and isotope ⁶³Ni was presented. In consideration of the isotope’s self-absorption effect, the current paper studied and analyzed the thickness of semiconductor and isotope source, PN junction depth, depletion region thickness, doping concentration, minority carrier diffusion length and the generation and collection of electron hole pairs with simulation of transport process of beta particles in semiconductor material using Monte-Carlo simulation program MCNP. The optimization output performances and corresponding parameter values of the microbattery under different junction depths were obtained. For the proposed design scheme, when the activity of radioisotope is 3.7×10⁷ Bq, and the surface area of PN junction is 0.01 cm², the optimization result is that short circuit current density, open circuit voltage, fill factor, maximum output power and efficiency of a single device are 379.68 nA/cm², 1.375 V, 84.39%, 440.4 nW/cm² and 4.34%, respectively.