A two-dimensional electron gas (2DEG) formed near a semiconductor surface has an advantage for the injection and detection of electron spins to realize a spin field-effect transistor (spin FET). Here, we investigated the strength of spin-orbit interaction (SOI) in 26.5nm In0:52Al0:48As and AlAs surface layer/5 nm InP/7.5 nm In0.53Ga0:47As/10nm In0.7Ga0.3As 2DEGs. By the selective wet etching of In0.52Al0.48As and InP layers, we achieved a 5nm InP/In0.53Ga0.47As/In0.7Ga0.3As 2DEG with a carrier density of 1:06× 1012 cm-2. Magnetoconductance is measured to evaluate the strength of Rashba SOI by the quantum correction of the conductance in the ballistic regime developed by Golub. The Rashba SOI parameter α reaches 3:85× 10-12 eV m, which yields a spin rotation angle of 2.34π within the elastic scattering length indicating a good candidate for the channel of a spin FET.