We show that the spin polarization of electron density in non-magnetic degenerate semiconductors can achieve 100%. The effect of 100% spin accumulation does not require a half-metallic ferromagnetic contact and can be realized in ferromagnet-semiconductor FM-n(+)-n junctions even at moderate spin selectivity of the FM-n(+) contact when the electrons with spin 'up' are extracted from n semiconductor through the heavily doped n(+) layer into the ferromagnet and the electrons with spin 'down' are accumulated near the n(+)-n interface. We derived a general equation relating spin polarization of the current to that of the electron density in non-magnetic semiconductors. We found that the effect of complete spin polarization is achieved near the n(+)-n interface when the concentration of the spin 'up' electrons tends to zero in this region while the diffusion current of these electrons remains finite.