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We have fabricated and characterized GaN-based vertical cavity surface emitting lasers (VCSELs) with a unique active region structure, in which three sets of InGaN asymmetric coupled quantum wells are placed in a half-wavelength (0.5λ) length. Lasing action was achieved under optical pumping at room temperature with a threshold pumping energy density of about 6.5 mJ/cm2. The laser emitted a blue light at 449.5 nm with a narrow linewidth below 0.1 nm and had a high spontaneous emission factor of about 3.0×10-2. The results indicate that this active region structure is useful in reducing the process difficulties and improving the threshold characteristics of GaN-based VCSELs. [ABSTRACT FROM AUTHOR]