Exemplary embodiments of the present invention relate to a method of growing gallium nitride-based semiconductor layers through metal-organic chemical vapor deposition, including disposing a substrate in a chamber, growing a first conductivity-type gallium nitride-based semiconductor layer on the substrate at a first chamber pressure, growing a gallium nitride-based active layer on the first conductivity-type gallium nitride-based semiconductor layer at a second chamber pressure higher than the first chamber pressure, and growing a second conductivity-type gallium nitride-based semiconductor layer on the active layer at a third chamber pressure lower than the second chamber pressure.