GaN-based LEDs were fabricated on patterned-sapphire substrates with various pyramidal-pattern coverage percentages (31-81). Three distinguish stages are observed in the behavior of the light out-put power against coverage percentage. By etching-pit density measurement, dislocation density is found to be independent with coverage percentage. The light extraction efficiency (LEE) should be the main mechanism for the enhancement in the light out-put power. LEE would be enhanced, when the pattern coverage is less than 39 or over 67. The light extraction efficiency remains similar, when the pattern coverage in between 39 ∼ 67.