We investigate the structural and electrical properties of polycrystalline 3C-SiC obtained from P ion implanted 4H-SiC with the box-shaped doping profile (NP: 6 x 1020/cm3, thickness: 400 nm, ion dose: 1.6 x 1016/cm2, room temperature). RBS measurement reveals that the highly defective region is formed by P ion implantation, which remains even after annealing at 1700 oC. X-TEM observation shows the P ion induced amorphous layer is recrystallized to twinned-3C-SiC. After annealing at 1300 oC, a sheet resistance of 950 /sq. and sheet carrier concentration of 1 x 1015/cm2 was obtained. By increasing the annealing temperature from 1500 to 1700 oC, the sheet resistance was drastically decreased to about 200 /sq., while there was a small change in the sheet carrier concentration. For the sample annealed at 1700 oC, the electrical activity of the P impurity was estimated to be about 10 % which is comparable to the case of hot implanted sample.