A polarization-resolved optical pumping investigation in a nonmagnetic semiconductor is performed. Spins are injected optically by a circularly polarized two-photon pumping in the samples. The injection of the electron spins is probed by measuring the polarization-resolved transmission of the samples. From the transmission data, the degree of spin-polarization of electrons is measured as a function of the time delay of the probe as well as of the temperature. The results show that the degree of spin-polarization is decreased with increasing temperature. The polarization decrease at higher temperatures might be due to the band-narrowing effect.