In the field of semiconductor spintronics, n-type GaAs has been utilized as a prototype system, where one can inject electronic spin and study its behavior with optical techniques. On the other hand MuSR should have sensitivity to the electronic spin polarization because muonium in mF = 0 or +1 has significant difference in the muon spin relaxation due to the hyperfine interaction, and exchanges its bound electron with local environment. In this proposal we demonstrate this principle using photo-MuSR technique with optical spin orientation, and investigate its mechanism using a computer modeling.