[en] Angular distribution of emitted protons was measured at a deuteron energy of 12.3 MeV. The energy levels of the ³¹Si nucleus were determined with high accuracy up to an excitation energy of 9 MeV. Thirty-four bound states and 47 unbound states were observed. The contribution of the direct process to the reaction is dominant. Therefore, DWBA (Distorted Wave Born Approximation) analysis was carried out for 14 bound states and 8 unbound states and the spectroscopic factors were calculated for them. Discrepancies in spectroscopic data obtained by different authors are discussed. For instance, for the 5.28 MeV state, the DWBA calculation gives a better fit for the transferred orbital momentum l = 1 than for l = 0. Improvement of the fit by choosing a different l value was also obtained for the levels of 5.95, 6.58, and 7.43 MeV