  Using an ultra sensitive magneto-optical Kerr rotation setup we have observed
electrical spin injection from (Zn,Mn)Se into bulk GaAs and quantified the spin
injection efficiency. The current induced contribution was carefully separated
from possible artifacts and studied as a function of voltage and external
magnetic field. Our measurements allow us to estimate the concentration of the
electrically injected spins into GaAs to be approximately
0.4$\times10^{15}$cm$^{-3}$ at a reverse bias of 0.7 V.
