We achieved spatially averaged hole concentrations above 10(19) cm(-3) at room temperature in Mg-doped InxGa1-xN/GaN (4nm/4nm) superlattices grown by metalorganic vapor phase epitaxy. The hole concentrations for the InxGa1-xN /GaN superlattices increased with the In mole fraction, and the maximum hole concentration reached 2.8 x 10(19) cm-3 for the In0.22Ga0.78N/GaN superlattice. The hole concentrations for the superlattices are larger than those for the InGaN bulk layers with the same average In mole fraction. The weak temperature dependence of the resistivities for InGaN/GaN superlattices with higher In mole fractions indicates highly efficient hole generation in the superlattice.