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GaN-based blue resonant-cavity light-emitting diodes (RCLEDs) have been fabricated by the two-step substrate transfer technique. The prefabricated structure was separated from its sapphire substrate by laser lift-off (LLO) process and was then transferred to a Si permanent substrate. By optimising the LLO process and adopting an indium tin oxide thin film and two high-reflectivity dielectric distributed Bragg reflectors, a narrow linewidth of 0.3 nm at 461.2 nm, corresponding to a quality factor of approximately 1530, has been observed from a blue RCLED under a current density of 2 kA/cm 2 . It indicates that a high quality optical resonator has been realised by this approach.Introduction: GaN-based materials have attracted increasing attention especially for light-emitting devices from the violet to green spectral region. Although blue light-emitting diodes and laser diodes have been commercialised, much effort is being made towards realisation of advanced devices such as resonant-cavity light-emitting diodes (RCLEDs) and vertical cavity surface-emitting lasers (VCSELs). For these devices, high quality optical resonators are required [1]. Recently, GaN-based blue RCLEDs have been reported where high quality optical resonators were realised using two high-reflectivity distributed Bragg reflectors (DBRs) [2-5]. Diagne et al. and Lu et al. demonstrated hybrid cavity RCLEDs composed of one monolithically grown nitride DBR and one dielectric DBR.However, a large layer number for high reflectivity is required owing to the small refractive index contrast between GaN and AlGaN. In addition, the large lattice mismatch between GaN and AlGaN (or AlN) can result in the formation of defects and the crystalline quality of multiple quantum wells (MQWs) grown consequently on such DBRs will be degraded. On the other hand, Song et al. obtained blue RCLEDs with two dielectric DBRs using electrodeposition, bonding and laser lift-off techniques. In this approach, however, it is difficult to bond the patterned structure onto a host substrate. Furthermore, it is necessary to perform dry etching to the Si-doped GaN layer for the n-contact and polishing process to get a smooth GaN surface before evaporation of the top dielectric DBR. As a result, the RCLED fabrication procedure becomes very complicated.