We report on residual impurities in semi-polar (3 0 (3) over bar (1) over bar) and (2 0 (2) over bar (1) over bar) GaN homo-epitaxial layer grown by metal-organic chemical vapor deposition. The (3 0 (3) over bar (1) over bar) and (2 0 (2) over bar (1) over bar) GaN layer showed atomically smooth surface and clear steps toward [1 0 (1) over bar 6] and [1 0 (1) over bar 4], respectively. The residual impurity concentrations of oxygen and carbon were below the detection limit of secondary-ion mass spectroscopy. Low-temperature photoluminescence revealed that (2 0 (2) over bar (1) over bar) GaN layer consisted free excitons and Si donor bound excitons, along with two-electron satellite lines and longitudinal optical (LO) phonon coupling transitions. The results indicate semi-polar (3 0 (3) over bar (1) over bar) and (2 0 (2) over bar (1) over bar) GaN epitaxial layers are promising candidates in obtaining a high quality GaN drift layer for vertical GaN devices.